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Full text of "NFPA NEC (1999): National Electrical Code"

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NOTICE OF INCORPORATION 

United States Legal Document 

£3P All citizens and residents are hereby advised that 
this is a legally binding document duly incorporated by 
reference and that failure to comply with such 
requirements as hereby detailed within may subject you 
to criminal or civil penalties under the law. Ignorance of 
the law shall not excuse noncompliance and it is the 
responsibility of the citizens to inform themselves as to 
the laws that are enacted in the United States of America 
and in the states and cities contained therein. ~*&k 

* * 

NFPA-70 (1999), the National Electrical Code, 
as incorporated by reference by the States and 
Municipalities and by the Code of Federal 
Regulations at 16 CFR 1211.2(c) and at 
7 CFR 1755.500(b) et. seq. 



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NEC1999 

National Electrical Code 



International Electrical Code™ Series 





♦. 



AN INTERNATIONAL CODES AND 
NFPA STANDARDS ORGANIZATION 




• 



• 



NEC1999 

National Electrical Code 



International Electrical Code™Series 





NFPA* 



AN INTERNATIONAL CODES AND 
STANDARDS ORGANIZATION 



NOTATIONS USED IN THIS CODE 
The following notations appear in this Code to aid the user: 
° A bullet in the margin indicates that material from the previous edition has been deleted. 

x A superscript "x" indicates that material has been extracted from other NFPA codes and standards. The 
source documents are identified in Appendix A. 

A vertical line in the margin indicates that the material differs from the previous edition. The user should 
inspect this text carefully, as some requirements may have changed. 



■i r**?**** ^ Copyright © 1998 

National Fire Protection Association, Inc. 
One Batterymarch Park 
Quincy, Massachusetts 02269 




IMPORTANT NOTICE ABOUT THIS DOCUMENT 

NFPA codes and standards, of which the document contained herein is one, are developed through a consensus stan- 
dards development process approved by the American National Standards Institute. This process brings together volun- 
teers representing varied viewpoints and interests to achieve consensus on fire and other safety issues. While the NFPA 
administers the process and establishes rules to promote fairness in the development of consensus, it does not indepen- 
dently test, evaluate, or verify the accuracy of any information or the soundness of any judgments contained in its codes 
and standards. 

The NFPA disclaims liability for any personal injury, property or other damages of any nature whatsoever, whether 
special, indirect, consequential or compensatory, directly or indirectly resulting from the publication, use of, or reliance 
on this document. The NFPA also makes no guaranty or warranty as to the accuracy or completeness of any informa- 
tion published herein. 

In issuing and making this document available, the NFPA is not undertaking to render professional or other services 
for or on behalf of any person or entity. Nor is the NFPA undertaking to perform any duty owed by any person or entity 
to someone else. Anyone using this document should rely on his or her own independent judgment or, as appropriate, seek 
the advice of a competent professional in determining the exercise of reasonable care in any given circumstances. 

The NFPA has no power, nor does it undertake, to police or enforce compliance with the contents of this document. 
Nor does the NFPA list, certify, test or inspect products, designs, or installations for compliance with this document. Any 
certification or other statement of compliance with the requirements of this document shall not be attributable to the NFPA 
and is solely the responsibility of the certifier or maker of the statement. 

See inside back cover for additional important notices and information. 



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For answers to all your Code questions, you 
can depend on the 1999 NEC* Handbook! 





The National Electrical Code® is the 
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The 1999 NEC Handbook covers 
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Get up-to-date on new Code requirements 

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70-1 



Copyright © 1998 NFPA, All Rights Reserved 

NFPA 70 

National Electrical Code® 

1999 Edition 

This edition of NFPA 70, National Electrical Code, was prepared by the National Electrical Code 
Committee and acted on by the National Fire Protection Association, Inc., at its Annual Meeting held 
May 18-21, 1998, in Cincinnati, OH. It was issued by the Standards Council on July 16, 1998, with 
an effective date of August 5, 1998, and supersedes all previous editions. 

This edition of NFPA 70 was approved as an American National Standard on August 6, 1998. 

History and Development of the National Electrical Code 

The National Fire Protection Association has acted as sponsor of the National Electrical Code since 
1911. The original Code document was developed in 1897 as a result of the united efforts of various 
insurance, electrical, architectural, and allied interests. 

~ In accordance with the provisions of the NFPA Regulations Governing Committee Projects, a 
National Electrical Code Committee Report on Proposals containing proposed amendments to the 1996 
National Electrical Code was published by the NFPA in June 1997. This report recorded the actions 
of the various Code-Making Panels and the Correlating Committee of the National Electrical Code 
Committee on each proposal that had been made to revise the 1996 Code. The report was circulated 
to all members of the National Electrical Code Committee and was made available to other interested 
NFPA members and to the public for review and comment. Following the close of the public comment 
period, the Code-Making Panels met, acted on each comment, and reported their action to the Correlating 
Committee. The NFPA published the National Electrical Code Committee Report on Comments in 
April 1998, which recorded the actions of the Code-Making Panels and the Correlating Committee on 
each public comment to the National Electrical Code Committee Report on Proposals. The National 
Electrical Code Committee Report on Proposals and the National Electrical Code Committee Report 
on Comments were presented to the 1998 NFPA Annual Meeting for adoption. 

NFPA has an Electrical Section that provides particular opportunity for NFPA members interested 
in electrical safety to become better informed and to contribute to the development of the National 
Electrical Code and other NFPA electrical standards. Each of the Code-Making Panels and the Chairman 
of the Correlating Committee reported their recommendations to meetings of the Electrical Section at 
the 1998 NFPA Annual Meeting. The Electrical Section thus had opportunity to discuss and review 
the report of the National Electrical Code Committee prior to the adoption of this edition of the Code 
by the Association. 

This 1999 edition supersedes all other previous editions, supplements, and printings dated 1897, 
1899, 1901, 1903, 1904, 1905, 1907, 1909, 1911, 1913, 1915, 1918, 1920, 1923, 1925, 1926, 1928, 
1930, 1931, 1933; 1935, 1937, 1940, 1942, 1943, 1947, 1949, 1951, 1953,' 1954, 1955, 1956, 1957, 
1958, 1959, 1962, 1965, 1968, 1971, 1975, 1978, 1981, 1984, 1987, 1990, 1993, and 1996. 

Changes in this 1999 edition of the National Electrical Code (as compared with the 1996 edition) 
are indicated by vertical lines in the margin. 

The location (in the 1996 edition) of material not appearing in the 1999 edition, and not identified 
as a change by a vertical line, is identified by a bullet (•) in the margin. Changes in section and table 
numbers are not identified. 

Material identified by the superscript letter ' 'x" includes text extracted from other NFPA documents 
as identified in Appendix A. / 

This Code is purely advisory as far as NFPA and ANSI are concerned, but is offered for use in 
law and for regulatory purposes in the interest of life and property protection. Anyone noticing any 
errors should notify the Secretary of the National Electrical Code Committee at the NFPA Executive 
Office. 



NATIONAL ELECTRICAL CODE 1999 Edition 



70-2 



CONTENTS 



CONTENTS 



ARTICLE 

90 Introduction 70-17 

Chapter 1 General. 

100 Definitions 70-19 

A. General 70-19 

B. Over 600 Volts, Nominal 70-25 

1 10 Requirements for Electrical Installations 70-26 

A. General . 70-26 

B. 600 Volts, Nominal, or Less 70-28 

C. Over 600 Volts, Nominal 70-30 

D. Tunnel Installations Over 600 Volts, Nominal . . . 70-32 

Chapter 2 Wiring and Protection 

200 Use and Identification of Grounded Conductors .... 70-35 

210 Branch Circuits 70-37 

A. General Provisions . 70-37 

B. Branch-Circuit Ratings. 70-41 

C. Required Outlets 70-43 

215 Feeders 70-46 

220 Branch-Circuit, Feeder, and Service Calculations . . . 70-48 

A. General .' 70-48 

B. Feeders and Services 70-49 

C. Optional Calculations for Computing Feeder 

and Service Loads 70-52 

D. Method for Computing Farm Loads 70-55 

225 Outside Branch Circuits and Feeders . 70-55 

A. General 70-56 

B. More than One Building or Other Structure .... 70-58 

C. Over 600 Volts 70-60 

230 Services 70-61 

A. General 70-61 

B. Overhead Service-Drop Conductors 70-62 

C. Underground Service-Lateral Conductors 70-63 

D. Service-Entrance Conductors 70-64 

E. Service Equipment — General 70-66 

F Service Equipment — Disconnecting Means . . . . 70-66 

G. Service Equipment — Overcurrent Protection . . . 70-68 

H. Services Exceeding 600 Volts, Nominal 70-69 

240 Overcurrent Protection 70-70 

A. General 70-70 

B. Location 70-73 

C. Enclosures. . .' •. 70-76 

• D. Disconnecting and Guarding 70-76 

E. Plug Fuses, Fuseholders, and Adapters 70-77 

F Cartridge Fuses and Fuseholders 70-77 

G. Circuit Breakers . . 70-78 

H. Supervised Industrial Installations 70-78 

I. Overcurrent Protection Over 600 Volts, 

Nominal . . . 70-80 

.250 Grounding 70-80 

A. General 70-80 

B. Circuit and System Grounding 70-83 

C. Grounding Electrode System and Grounding 

Electrode Conductor 70-88 

D. Enclosure, Raceway, and Service Cable 

Grounding 70-91 

E. Bonding 70-92 



ARTICLE 

F. Equipment Grounding and Equipment Grounding 
Conductors 70-94 

G. Methods of Equipment Grounding 70-98 

H. Direct-Current Systems :70-100 

J. Instruments, Meters, and Relays ; .70-101 

K. Grounding of Systems and Circuits of 1 kV and 

Over (High Voltage) 70-102 

280 Surge Arresters .:..., 70-103 

A. General. 70-103 

B. Installation ' : .70-104 

C. Connecting Surge Arresters 70-104 

Chapter 3 Wiring Methods and Materials 

300 Wiring Methods 70-105 

A. General Requirements :70-105 

B. Requirements for Over 600 Volts, Nominal . . . .70-113 

305 Temporary Wiring , 70-115 

310 Conductors for General Wiring . . . . .70-116 

318 Cable Trays 70-140 

320 Open Wiring on Insulators • • • .70-146 

321 Messenger Supported Wiring .70-147 

324 Concealed Knob-and-Tube Wiring 70-148 

325 Integrated Gas Spacer Cable 70-149 

A. General . .' 70-149 

B. Installation 70-150 

C. Construction Specifications 70-150 

326 Medium Voltage Cable : 70-150 

328 Flat Conductor Cable. 70-151 

A. General 70-151 

B. Installation 70-151 

C. Construction . . _ 70-152 

330 Mineral-Insulated, Metal-Sheathed Cable 70-153 

A. General .70-153 

B. Installation . . . 70-153 

C. Construction Specifications 70-154 

331 Electrical Nonmetallic Tubing 70-154 

A. General , 70-154 

B. Installation 70-155 

C. Construction Specifications 70-155 

333 Armored Cable .70-155 

A. General 70-155 

B. Installation 70-156 

C. Construction Specifications 70-157 

334 Metal-Clad Cable 70-157 

A. General 70-157 

B. Installation 70-157 

C. Construction Specifications 70-158 

336 Nonmetallic-Sheathed Cable 70-159 

A. General. ........:..: 70-159 

B. Installation .70-159 

C. Construction Specifications 70-160 

338 Service-Entrance Cable . . .70-161 

339 Underground Feeder and Branch-Circuit Cable . . . .70-162 

340 Power and Control Tray Cable . . . % ...... . .70-162 



1999 Edition 



NATIONAL ELECTRICAL CODE 



CONTENTS 



70-3 



• 



ARTICLE 

342 Nonmetallic Extensions 70-163 

343 Nonmetallic Underground Conduit with 

Connectors 70-164 

A. General 70-164 

B. Installation 70-165 

C. Construction 70-165 

345 Intermediate Metal Conduit 70-166 

A. General. . .70-166 

B. Installation 70-166 

C. Construction Specifications . 70-167 

Q 

346 Rigid Metal Conduit 70-167 

A. General 70-167 

B. Installation . .70-168 

C. Construction Specifications . '. 70-169 

347 Rigid Nonmetallic Conduit 70-169 

A. Installations 70-170 

B. Construction Specifications 70-172 

348 Electrical Metallic Tubing 70-172 

A. General 70-172 

B. Installation . 70-173 

C. Construction Specifications 70-174 

349 Flexible Metallic Tubing .70-174 

A. General 70-174 

B. Construction and Installation 70-174 

350 Flexible Metal Conduit 70-175 

A. General 70-175 

B. Installation . .70-175 

351 Liquidtight Flexible Metal Conduit and Liquidtight 

Flexible Nonmetallic Conduit 70-176 

A. Liquidtight Flexible Metal Conduit. ...... .70-176 

B. Liquidtight Flexible Nonmetallic Conduit 70-177 

352 Surface Metal Raceways and Surface Nonmetallic 
Raceways .70-178 

A. Surface Metal Raceways 70-178 

B. Surface Nonmetallic Raceways 70-179 

C. Strut-Type Channel Raceway 70-180 

353 Multioutlet Assembly 70-181 

354 Underfloor Raceways 70-181 

356 Cellular Metal Floor Raceways 70-183 

A. Installation ................ .70-183 

B. Construction Specifications 70-183 

358 Cellular Concrete Floor Raceways . . . 70-184 

362 Metal Wireways and Nonmetallic Wireways 70-184 

A. Metal Wireways 70-184 

B. Nonmetallic Wireways 70-186 

363 Flat Cable Assemblies 70-187 

364 Busways 70-188 

A. General Requirements 70-188 

B. Requirements for Over 600 Volts, Nominal . . . .70-189 

365 Cablebus 70-190 

370 Outlet, Device, Pull and Junction Boxes, Conduit 

Bodies and Fittings .70-191 

A. Scope and General 70-191 

B. Installation 70-192 

C. Construction Specifications 70-197 

D. Manholes and Other Electric Enclosures Intended 

for Personnel Entry . .70-197 



ARTICLE 

E. Pull and Junction Boxes for Use on Systems 

Over 600 Volts, Nominal 70-199 

373 Cabinets, Cutout Boxes, and Meter Socket 

Enclosures 70-199 

A. Installation 70-199 

B. Construction Specifications . 70-201 

374 . Auxiliary Gutters . 70-202 

380 Switches. ..-..' , 70-204 

A. Installation 70-204 

B. Construction Specifications 70-207 

384 Switchboards and Panelboards 70-207 

A. General 70-207 

B. Switchboards . .70-208 

C. Panelboards .70-208 

D. Construction Specifications .70-210 

Chapter 4 Equipment for General Use 

400 Flexible Cords and Cables . .70-211 

A. General. 70-211 

B. Construction Specifications . . . . .70-220 

C. Portable Cables Over 600 Volts, Nominal 70-221 

402 . Fixture Wires . 70-221 

410 Lighting Fixtures, Lampholders, Lamps, and 

Receptacles 70-225 

A. General 70-225 

B. Fixture Locations 70-225 

C. Provisions at Fixture Outlet Boxes, Canopies, 

and Pans . .70-226 

D. Fixture Supports 70-227 

E. Grounding 70-227 

F. Wiring of Fixtures 70-228 

G. Construction of Fixtures 70-229 

H. Installation of Lampholders 70-230 

J. Construction of Lampholders 70-230 

K. Lamps and Auxiliary Equipment. 70-23 1 

L. Receptacles, Cord Connectors, and Attachment 

Plugs (Caps). .70-231 

M. Special Provisions for Flush and Recessed 

Fixtures 70-232 

N. Construction of Flush and Recessed Fixtures . . . .70-233 
P. Special Provisions for Electric-Discharge ■ 

Lighting Systems of 1000 Volts or Less 70-233 

Q. Special Provisions for Electric-Discharge 

Lighting Systems of More Than 100 Volts 70-234 

R. Lighting Track 70-235 

411 Lighting Systems Operating at 30 Volts or Less . . . .70-236 

422 Appliances 70-236 

A. General 70-236 

B. Installation 70-236 

C. Disconnecting Means 70-239 

D. Construction .70-240 

E. Marking 70-241 

424 Fixed Electric Space-Heating Equipment 70-241 

A. General 70-241 

B. Installation '. 70-242 

C. Control and Protection of Fixed Electric 
Space-Heating Equipment .70-242 

D. Marking of Heating Equipment ........ .70-244 

E. Electric Space-Heating Cables 70-244 

F. Duct Heaters. . .70-246 

G. Resistance-Type Boilers .70-246 

H. Electrode-Type Boilers 70-247 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-4 



CONTENTS 



J. Electric Radiant Heating Panels and Heating 

Panel Sets 70-248 

426 Fixed Outdoor Electric Deicing and Snow-Melting 
Equipment 70-250 

A. General 70-250 

B. Installation .70-251 

C. Resistance Heating Elements 70-251 

D. Impedance Heating .70-252 

E. Skin-Effect Heating 70-252 

F. Control and Protection , .70-253 

427 Fixed Electric Heating Equipment for Pipelines 

and Vessels 70-253 

A. General . .70-253 

B. Installation .70-254 

C. Resistance Rating Elements 70-254 

D. Induction Heating. 70-255 

F. Skin-Effect Heating .70-255 

G Control and Protection . . . . 70-256 

430 Motors, Motor Circuits, and Controllers ...... .70-256 

A. General 70-256 

B. Motor Circuit Conductors 70-262 

C. Motor and Branch-Circuit Overload 

Protection 70-264 

D. Motor Branch-Circuit Short-Circuit and 

Ground-Fault Protection .70-267 

E. Motor Feeder Short-Circuit and Ground-Fault 
Protection 70-270 

F Motor Control Circuits 70-270 

G. Motor Controllers .70-272 

H. Motor Control Centers . . . ... . 70-273 

J. Disconnecting Means .70-275 

K. Over 600 Volts, Nominal 70-278 

L. Protection of Live Parts — All Voltages ..... .70-278 

M. Grounding — All Voltages 70-279 

N. Tables 70-280 

440 Air-Conditioning and Refrigeration Equipment . . . .70-283 

A. General .70-283 

B. Disconnecting Means 70-285 

C. Branch-Circuit Short-Circuit and Ground-Fault 
Protection • 70-286 

D. Branch-Circuit Conductors 70-287 

E. Controllers for Motor-Compressors 70-287 

F. Motor-Compressor and Branch-Circuit Overload 
Protection 70-288 

G. Provisions for Room Air Conditioners 70-289 

445 Generators 70-289 

450 Transformers and Transformer Vaults (Including 

Secondary Ties) .70-290 

A. General Provisions 70-291 

B. Specific Provisions Applicable to Different Types 

of Transformers .70-295 

C. Transformer Vaults 70-296 

455 Phase Converters 70-297 

A. General 70-297 

B. Specific Provisions Applicable to Different 

Types of Transformers 70-299 

460 Capacitors . .70-299 

A. 600 Volts, Nominal, and Under ........ .70-299 

B. Over 600 Volts, Nominal. . 70-300 

470 Resistors and Reactors .70-301 

A. 600 Volts, Nominal, and Under ........ .70-301 

B. Over 600 Volts, Nominal .70-301 

480 Storage Batteries 70-301 



ARTICLE 
490 



500 

501 
502 

503 
504 
505 
510 
511 
513 
514 
515 
516 

517 



518 
520 



525 



530 



Equipment, Over 600 Volts, Nominal 70-303 

A. General 70-303 

B. Equipment — Specific Provisions 70-303 

C. Equipment — Metal-Enclosed Power Switchgear 

and Industrial Control Assemblies 70-305 

D. Mobile and Portable Equipment 70-307 

E. Electrode-Type Boilers 70-308 

Chapter 5 Special Occupancies 

Hazardous (Classified) Locations, Classes I, II, and In, 
Divisions 1 and 2 .."........ .70-309 

Class I Locations , .70-315 

Class II Locations 70-324 

Class III Locations .70-330 

Intrinsically Safe Systems 70-333 

Class I, Zone 0, 1, and 2 Locations . .70-335 

Hazardous (Classified) Locations — Specific 70-342 

Commercial Garages, Repair and Storage .70-343 

Aircraft Hangars 70-344 

Gasoline Dispensing and Service Stations 70-346 

Bulk Storage Plants 70-350 

Spray Application, Dipping, and Coating 

Processes 70-353 

Health Care Facilities 70-359 

A. General 70-359 

B. Wiring and Protection 70-361 

C. Essential Electrical System .70-364 

D. Inhalation Anesthetizing Locations 70-372 

E. X-Ray Installations 70-375 

F. Communications, Signaling Systems, Data 
Systems, Fire Alarm Systems, and Systems Less 

than 120 Volts, Nominal •. . .70-376 

G. Isolated Power Systems 70-377 

Places of Assembly 70-378 

Theaters, Audience Areas of Motion Picture and 

Television Studios, and Similar Locations 70-379 

A. General 70-379 

B. Fixed Stage Switchboards 70-380 

C. Fixed Stage Equipment Other than 

Switchboards 70-381 

D. Portable Switchboards on Stage 70-383 

E. Portable Stage Equipment Other than 

Switchboards 70-386 

F. Dressing Rooms .70-387 

G. Grounding 70-387 

Carnivals, Circuses, Fairs, and Similar Events. . . . .70-387 

A. General Requirements 70-387 

B. Installation 70-388 

C. Grounding and Bonding 70-389 

D. Disconnecting Means 70-389 

E. Attractions Utilizing Pools, Fountains, and 
Similar Installations with Contained Volumes of 

Water. 70-389 

Motion Picture and Television Studios and Similar 

Locations .70-389 

A. General 70-389 

B. Stage or Set ... .70-390 

C. Dressing Rooms .70-393 



1999 Edition 



NATIONAL ELECTRICAL CODE 



CONTENTS 



70-5 



• 



ARTICLE 

D. Viewing, Gutting, and Patching Tables ..... .70-393 

E. Cellulose Nitrate Film Storage Vaults .70-393 

F. Substations 70-393 

G. Separately Derived Systems with 60 Volts to 

Ground 70-393 

540 Motion Picture Projectors 70-394 

A. General 70-394 

B. Definitions . .70-394 

C. Equipment and Projectors of the Professional 

Type 70-394 

D. Nonprofessional Projectors 70-395 

E. Audio Signal Processing, Amplification, and 
Reproduction Equipment 70-395 

545 Manufactured Building ; . 70-395 

A. General } 70-395 

547 Agricultural Buildings . . 70-396 

550 Mobile Homes, Manufactured Homes, and Mobile 

Home Parks 70-398 

A. General 70-398 

B. Mobile Homes . .70-399 

C. Services and Feeders .70-406 

551 Recreational Vehicles and Recreational Vehicle 

Parks ... . ... . . . . . .70-407 

A. General .70-407. 

B. Low- Voltage Systems 70-408 

C. Combination Electrical Systems '.. 70-410 

D. Other Power Sources .70-410 

E. Nominal 120- Volt or 120/240- Volt Systems . . . .70-411 

F. Factory Tests 70-418 

. G. Recreational Vehicle Parks 70-418 

552 Park Trailers 70-420 

A. General 70-420 

B. Low- Voltage Systems .70-421 

C. Combination Electrical Systems 70-422 

D. Nominal 120- Volt or 120/240- Volt Systems . . . .70-423 

E. Factory Tests .70-429 

553 Floating Buildings .70-430 

A. General 70-430 

B. Services and Feeders . .' 70-430 

C. Grounding. 70-430 

555 Marinas and Boatyards 70-431 

Chapter 6 Special Equipment 

600 Electric Signs and Outline Lighting 70-433 

A. General. . 70-433 

B. Field-Installed Skeleton Tubing .70-435 

604 Manufactured Wiring Systems 70-437 

605 Office Furnishings (Consisting of Lighting 

Accessories and Wired Partitions) .70-437 

610 Cranes and Hoists .70-438 

A. General 70-438 

B. Wiring 70-439 

C. Contact Conductors 70-441 

D. Disconnecting Means 70-442 

E. Overcurrent Protection 70-442 

F. Control .' 70-443 

G. Grounding. 70-443 

620 Elevators, Dumbwaiters, Escalators, Moving Walks, 

Wheelchair Lifts, and Stairway Chair Lifts 70-444 

A. General • 70-444 



B. Conductors 70-445 

C. Wiring 70-446 

D. Installation of Conductors 70-448 

E. Traveling Cables 70-449 

F. Disconnecting Means and Control . . . '". . . . .70-450 

G. Overcurrent Protection . . 70-451 

H. Machine Room 70-451 

J. Grounding 70-452 

K. Emergency and Standby Power Systems 70-452 

625 Electric Vehicle Charging System Equipment 70^52 

A. General. 70-452 

B. Wiring Methods 70-453 

C. Equipment Construction 70-453 

D. Control and Protection 70-454 

E. Electric Vehicle Supply Equipment 

Locations 70-454 

630 Electric Welders . 70-455 

A. General 70-455 

B. Arc Welders . . : .70-455 

C. Resistance Welders 70-456 

D. Welding Cable 70-457 

640 Audio Signal Processing, Amplification, and 

Reproduction Equipment ..'...■ 70-458 

A. General . . . ' 70-458 

B. Permanent Audio System Installations 70-461 

C. Portable and Temporary Audio System 

Installations . . 70-462 

645 Information Technology Equipment 70-463 

650 Pipe Organs .70-464 

660 X-Ray Equipment . . . .' 70-465 

A. General 70-465 

B. Control . 70^166 

C. Transformers and Capacitors 70-467 

D. Guarding and Grounding 70-467 

665 Induction and Dielectric Heating Equipment 70-467 

A. General. 70-467 

B. Guarding, Grounding, and Labeling 70-467 

C. Motor-Generator Equipment 70-468 

D. Equipment Other than Motor-Generators 70-469 

668 Electrolytic Cells .70-469 

669 Electroplating 70-472 

670 Industrial Machinery 70-473 

675 Electrically Driven or Controlled Irrigation 

Machines .70-474 

A. General. . 70^74 

B. Center Pivot Irrigation Machines 70-476 

680 Swimming Pools, Fountains, and Similar 

Installations 70-476 

A. General 70-476 

B. Permanently Installed Pools 70-480 

C. Storable Pools 70-484 

D. Spas and Hot Tubs 70-48.5 

E. Fountains : 70-486 

F. Pools and Tubs for Therapeutic Use 70-487 

G. Hydromassage Bathtubs 70-488 

685. Integrated Electrical Systems .70-489 

A. General 70-489 

B. Orderly Shutdown 70-489 

690 Solar Photovoltaic Systems 70-489 

A. General 70-489 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-6 



CONTENTS 



ARTICLE 

B. Circuit Requirements . 70-492 

C. Disconnecting Means . .70-493 

D : Wiring Methods . .70-494 

E. Grounding. .' 70-495 

F. Marking '.' 70-495 

G. Connection to Other Sources 70-496 

H. Storage Batteries 70-496 

I. Systems Over 600 Volts ; 70-497 

695 Fire Pumps. . . .70-497 

Chapter 7 Special Conditions 

700 Emergency Systems .70-501 

A. General ; 70-501 

B. Circuit Wiring 70-502 

C. Sources of Power 70-503 

D. Emergency System Circuits for Lighting and 

- Power ......' ' 70-504 

' E. Control — Emergency Lighting Circuits 70-504 

F Overcurrent Protection 70-505 

701 Legally Required Standby Systems 70-505 

A. General 70-505 

B. Circuit Wiring 70-506 

C. Sources of Power 70-506 

D. Overcurrent Protection 70-507 

702 Optional Standby Systems. 70-507 

A. General. . 70-507 

B. Circuit Wiring 70-508 

705 Interconnected Electrical Power Production 

Sources .70-508 

. 720 Circuits and Equipment Operating at Less than 

50 Volts . . . 70-510 

725 Class 1 , Class 2, and Class 3 Remote-Control, 

Signaling, and Power-Limited Circuits 70-510 

A. General 70-510 

B. Class 1 Circuits . . '. 70-511 

C. Class 2 and Class 3 Circuits 70-513 

727 Instrumentation Tray Cable: Type ITC 70-518 

760 Fire Alarm Systems . : 70-519 

A. General . . .70-519 

B. Nonpower-Limited Fire Alarm (NPLFA) 

Circuits 70-520 

C. Power-Limited Fire Alarm (PLFA) Circuits . . . .70-523 

770 Optical Fiber Cables and Raceways ......".. .70-527 

A. General 70-527 

B. Protection 70-528 

C. Cables Within Buildings 70-528 

780 Closed-Loop and Programmed Power 

Distribution. . . . .70-531 

Chapter 8 Communications Systems 

800 Communications Circuits 70-533 

A. General. . .70-533 



B. Conductors Outside and Entering Buildings . . . .70-533 

C. Protection 70-535 

D. Grounding Methods • :.. . .70-536 

E. Communications Wires and Cables Within 

. Buildings .70-537 

810 Radio and Television Equipment . .70-541 

A. General 70-541 

B. Receiving Equipment — Antenna Systems . ... .70-542 

C. Amateur Transmitting and Receiving 

Stations — Antenna Systems 70-544 

. D., Interior Installation — Transmitting Stations . . . .70-544 

820 Community Antenna Television and Radio Distribution 

Systems 70-545 

A. General 70-545 

B. Cables Outside and Entering Buildings . "" 70-545. 

C. Protection 70-546 

D. Grounding Methods 70-547 

E. Cables Within Buildings 70-548 

830 Network-Powered Broadband Communications 

Systems .70-550 

A. General . 70-550 

B. Cables Outside and Entering Buildings 70-552 

, C: Protection 70-554 

D. Grounding Methods . . .70-556 

E. Network-Powered Broadband Communications 

Systems Wiring Methods Within Buildings . . . .70-557 

Chapter 9 Tables 

Table 1 . Percent of Cross Section of Conduit and Tubing 

for Conductors 70-561 

Table 4. Dimensions and Percent Area of Conduit 

and Tubing 70-562 

Table 5. Dimensions of Insulated Conductors 

and Fixture Wires 70-564 

Table 5A. Compact Aluminum Building 

Wire Nominal Dimensions and Areas 70-566 

Table 8. Conductor Properties 70-567 

Table 9. Alternating-Current Resistance and Reactance 

for 600- Volt Cables, 3-Phase, 60 Hz, 75°C 

(167°F) — Three Single Conductors in 

Conduit. .70-568 

Table 11(a). Class 2 and Class 3 Alternating-Current 

Power Source Limitations 70-569 

Table 11(b). Class 2 and Class 3 Direct-Current Power 

Source Limitations 70-569 

Table 12(a). PLFA Alternating-Current Power Source 

Limitations -. . . .70-570 

Table 12(b). PLFA Direct-Current Power 

Source Limitations . .70-570 

Appendix A 70-571 

Appendix B .70-575 

Appendix C • 70-585 

Appendix D 70-609 

Appendix E '. 70-617 

Index 70-619 



1999 Edition 



NATIONAL ELECTRICAL CODE 



NATIONAL ELECTRICAL CODE COMMITTEE 



70-7 



• 



NATIONAL ELECTRICAL CODE COMMITTEE 

These lists represent the membership at the time each Committee was balloted on the text of this edition. Since 
that time, changes in the membership may have occurred. A key to classifications is found at the back of this 
document. 

Technical Correlating Committee 

D. Harold Ware, Chair [IM] 

Libra Electric Co., OK 

Rep. National Electrical Contractors Association 

Mark W. Earley, Secretary 

National Fire Protection Association 

(nonvoting) 

Jean A. O'Connor, Recording Secretary 

National Fire Protection Association 

(nonvoting) 



James E. Brunssen, Bell Communications Research (Bellcore), NJ [UT] 

Rep. Alliance for Telecommunications Industry Solutions 
Philip H. Cox, Int'l Association of Electrical Inspectors, TX [E] 

Rep. Int'l Association of Electrical Inspectors 
Dale R. Deming, AM Electric Co. (T&B), MI [M] 

Rep. National Electrical Manufacturers Association 
William R. Drake, Marinco, CA [M] 
Paul Duks, Underwriters Laboratories Inc., IL [RT] 
Joseph E. Pipkin, U.S. Dept. of Labor OSHA, Washington, DC [E] 
John W. Troglia, Edison Electric Institute, WI [UT] 

Rep. Edison Electric Institute 
John P. Widener, Jr., IBEW, Washington DC [L] 

Rep. Int'l Brotherhood of Electrical Workers 

Alternates 

David P. Brown, Baltimore Gas & Electric Co., MD [UT] 

(Alt. to J. W. Troglia) . 
Douglas A. Fisher, IBEW, Washington, DC [L] 

(Alt. to J. P. Widener, Jr..) 



Edward C. Lawry, Madison, WI [E] 

(Alt. to. P. H. Cox) 
W. Terry Lindsay, Duncan Electric Co. Inc., TN [IM] 

(Alt. to D. H. Ware) 
Keku M. Mistry, Bell Communications Research (Bellcore), NJ [RT] 

(Alt. to J. E. Brunssen) 
James T. Pauley, Square D Co., KY [M] 

(Alt. to D. R. Deming) 
Robert J. Pollock, Underwriters Laboratories Inc., IL [RT] 

(Alt. to P. Duks) 
Craig M. Wellman, DuPont Engineering, DE [U] 

(Voting Alt. to CMA Rep.) 

Nonvoting 

Richard G. Biermann, Biermann Electric Co. Inc., IA 
(Member Emeritus) 



CODE-MAKING PANEL NO. 1 
Articles 90, 100, 110 

Philip H. Cox, Acting Chair [E] 
Int'l Association of Electrical Inspectors, TX 
Rep. Int'l Association of Electrical Inspectors 



Richard G. Biermann, Biermann Electric Co. Inc., IA [IM] 

Rep. National Electrical Contractors Association 
H. Landis Floyd, II, The DuPont Co., DE [U] 

Rep. Institute of Electrical & Electronics Engineers, Inc. 
Don B. Ivory, Idaho Electrical JATC, ID [L] 

Rep. Int'l Brotherhood of Electrical Workers 
John D. Minick, National Electrical Manufacturers Association, TX [M] 

Rep. National Electrical Manufacturers Association 
Lyman L. Parks, Canadensis, PA [UT] 

Rep. Alliance for Telecommunications Industry Solutions/Bellcore 
Charles L. Roach, Eastman Chemical Co., TN [U] 

Rep. Chemical Manufacturers Association 
Steven G. Roll, Intertek Testing Services NA, Inc., MA [RT] 
John W. Troglia, Edison Electric Institute, WI [UT] 

Rep. Edison Electric Institute 
Robert A. Williams, Underwriters Laboratories Inc., NC [RT] 
Michael P. Wissman, Northern KY Electric Service, KY [IM] 

Rep. Independent Electrical Contractors 

Alternates 

David P. Brown, Baltimore Gas & Electric Co., MD [UT] 
(Alt. to J. W. Troglia) 



Paul Duks, Underwriters Laboratories Inc., IL [RT] 

(Alt. to R. A. Williams) 
James William Evans, Southport Electrical Inc., NC [IM] 

(Alt. to M. P. Wissman) 
Russell J. Helmick, Jr., City of Irvine, CA [E] 

(Alt. to P. H. Cox) 
Donald H. McCullough II, Westinghouse Savannah River Co., SC [U] 

(Alt. to H. L. Floyd, II) 
Deborah A. McDaniel, ICI Americas, DE [U] 

(Alt. to C. L. Roach) 
Larry Miller, National Electrical Manufacturers Association, VA [M] 

(Alt. to J. D. Minick) 
Keku M. Mistry, Bell Communications Research (Bellcore), NJ [UT] 

(Alt. to L. L. Parks) 
Ricky L. Oakland, IBEW, WY [L] 

(Alt. to D. B. Ivory) 
H. Brooke Stauffer, National Electrical Contractors Association, MD [EM] 

(Alt. to R. G. Biermann) 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70- 



NATIONAL ELECTRICAL CODE COMMITTEE 



CODE-MAKING PANEL NO. 2 

Articles 210, 215, 220, Appendix D Examples Dl through D6 

James W. Carpenter, Chair [E] 

North Carolina Dept. of Insurance, NC 

Rep. Int'l Association of Electrical Inspectors 



Richard W. Becker, Engineered Electrical Systems, Inc., WA [U] 

Rep. Institute of Electrical & Electronics Engineers, Inc. 
Thomas L. Harman, University of Houston - Clear Lake, TX [SE] 
Billy H. McClendon, PPG Industries, Inc., LA [U] 

Rep. Chemical Manufacturers Association 
Bernard Mericle, IBEW, NY [L] 

Rep. Int'l Brotherhood of Electrical Workers 
Donald A. Nissen, Underwriters Laboratories Inc., IL [RT] 
Gary J. O'Neil, Southern California Edison Co., CA [UT] 

Rep. Edison Electric Institute 
Earl W; Roberts, REPTEC, CT [M] 

Rep. National Electrical Manufacturers Association 
Albert F. Sidhom, U.S. Army Corps of Engineers, CA [U] 
Michael D. Toman, MEGA Power Electrical Services, Inc., MD [IM] 

Rep. National Electrical Contractors Association 
Robert G. Wilkinson, Independent Electrical Contractors of Houston, Inc., 

TX [IM] 

Rep. Independent Electrical Contractors 



Alternates 

Ernest S. Broome, City of Knoxville, TN [E] 

(Alt. to J. W. Carpenter) 
Thomas J. Castor, American Electric. Power Service Corp., OH [UT] 

(Alt. to G. J. O'Neil) 
Ernie Howell, IEC, Rocky Mountain Chapter, CO [IM] 

(Alt. to R. G. Wilkinson) 
James R. Jones, University of Alabama at Birmingham, AL [U] 

(Alt. to R. W. Becker) 
Charles D. Marshall, Jr., IBEW Local 948, MI [L] 

(Alt. to B. Mericle) 
James T. Pauley, Square D Co., KY [M] 

(Alt. to E. W. Roberts) 
Joseph Patterson Roche, Celanese Acetate, SC [U] 

(Alt. to B. H. McClendon) 
J. Morris Trimmer, University of Florida, FL [SE] 

(Alt. to T L. Harman) 



CODE-MAKING PANEL NO. 3 

Articles 300, 305, 690 

Raymond W. Weber, Chair [E] 

Dept. of Commerce, WI 

Rep. Int'l Association of Electrical Inspectors 



Joseph J. Andrews, Westinghouse Savannah River Co., SC [U] 

Rep. Institute of Electrical & Electronics Engineers, Inc. 
Charles W. Beile, Allied Tube & Conduit/Tyco, IL [M] 

Rep. National Electrical Manufacturers Association 
Ward I. Bower, Sandia National Laboratories, NM [U] 

Rep. Solar Energy Industries Association (VL 690) 
Michael I. Callanan, National Joint Apprentice & Training Committee, 

PA[L] 

Rep. Int'l Brotherhood of Electrical Workers 
C. Wiley Cruise, Duke Power Co., NC [UT] 

Rep. Edison Electric Institute 
Paul Duks, Underwriters Laboratories Inc., IL [RT] 
Charles E. Jackson, Hoechst Celanese Chemical Group, TX [U] 

Rep. Chemical Manufacturers Association 
Richard A. Pruzick, PC Electrical Construction, Inc., NJ [IM] 

Rep. National Electrical Contractors Association 
Edwin K. Rodkey, Carlon Electrical Products, A Lamson & Sessions Co., 

OH [M] 

Rep. Society of the Plastics Industry, Inc. '. 

Alternates 

Joseph V. Egan, IBEW Local 456, NJ [L] 
(Alt. to M. I. Callanan) 



Jack A. Gruber, Wheatland Tube Co., PA [M] 

(Voting Alt. to AISI Rep.) 
Dennis B. Horman, PacifiCorp (Utah Power/Pacific Power), UT [UT] 

(Alt. to C. W. Cruise) 
David H. Kendall, Carlon Electrical Products, A Lamson & Sessions Co.. 

OH [M] 

(Alt. to E. K. Rodkey) 
Allen F. KnicKrehm, The KnicKrehm Co., CA [IM] 

(Alt. to R. A. Pruzick) 
Richard P. Owen, City of St. Paul, MN [E] 

(Alt. to R. W. Weber) 
David A. Pace, Oli'n Corporation, AL [U] 

(Alt. to C. E. Jackson) 
Ken A. Rogers, Thomas & Betts Corp., TN [M] 

(Alt. to C. W. Beile) 
Melvin K. Sanders, Things Electrical Co., Inc., (TECo., Inc), IA [U] 

(Alt. to J. J. Andrews) 
Robert H. Wills, Advanced Energy Systems Inc., NH [U] 

(Alt. to W. I. Bower) (VL 690) 



CODE-MAKING PANEL NO. 4 
Articles 225, 230 

C. John Beck, Chair [UT] 

Pacific Gas and Electric Co., CA 

Rep. Edison Electric Institute 



Malcolm Allison, Gould Shawmut, MA [M] 

K. W. Carrick, Electrical Engineering Professional Services, Inc., MS [U] 

Rep. Institute of Electrical & Electronics Engineers, Inc. 
E. T. Dickerson, University of Houston - Clear Lake, TX [IM] 

Rep. Independent Electrical Contractors 



Floyd C. Ferris, New York Board of Fire Underwriters, NY [E] 
Howard D. Hughes, Hughes Electric Co. Inc., AR [IM] 

Rep. National Electrical Contractors Association 
James Lee Hunter, Southwire Co., GA [M] 

Rep. The Aluminum Association 



1999 Edition 



NATIONAL ELECTRICAL CODE 



NATIONAL ELECTRICAL CODE COMMITTEE 



70-9 



• 



William M. Lewis, Eli Lilly & Co., IN [U] 

Rep. Chemical Manufacturers Association 
Robert J. Pollock, Underwriters Laboratories Inc., IL [RT] 
Donald R. Strassburg, State of Washington, WA [E] 

Rep. Int'l Association of Electrical Inspectors 
Mark H. Sumrall, IBEW Local 527, TX [L] 

Rep. Int'l Brotherhood of Electrical Workers 
John W. Young, Siemens Energy & Automation, Inc., GA [M] 

Rep. National Electrical Manufacturers Association 

Alternates 

Thomas L. Adams, Commonwealth Edison, IL [UT] 
(Alt. to C. J. Beck) 



Hugh D. Butler, Jr., Southwire, GA [M] 

(Alt. to J. L. Hunter) 
Dennis Darling, Ayres, Lewis, Norris, & May, Inc., MI [U] 

(Alt. to K. W Carrick) 
Junior L. Owings, State of Oregon, OR [E] 

(Alt. to D. R. Strassburg) 
Philip M. Piqueira, General Electric Co., CT [M] 

(Alt. to J. W. Young) 
Ralph C. Prichard, Hercules Inc., DE [U] 

(Alt. to W. M. Lewis) 
William J. Tipton, IBEW, OH [L] 

(Alt. to M. H. Sumrall) 



CODE-MAKING PANEL NO. 5 
Articles 200, 250, 280, Appendix E 

J. Philip Simmons, Acting Chair [E] 
Int'l Association of Electrical Inspectors, WA 
Rep. Int'l Association of Electrical Inspectors 



Jeffrey Boksiner, Bell Communications Research (Bellcore), NJ [UT] 

Rep. Alliance for Telecommunications Industry Solutions 
Elio L. Checca, U.S. Dept. of Labor, VA [E] 
David A. Dini, Underwriters Laboratories Inc., IL [RT] 
Dan Hammel, Int'l Brotherhood of Electrical Workers, Local 704, IA [L] 

Rep. Int'l Brotherhood of Electrical Workers 
Charles F. Mello, Electro-Test, Inc., OR [IM] 

Rep. Int'l Electrical Testing Association Inc. 
Elliot Rappaport, Electro Technology Consultants, Inc., MI [U] 

Rep. Institute of Electrical & Electronics Engineers, Inc. 
Ted G. Robertson, Robertson Electric, Inc., TX [IM] 

Rep. Independent Electrical Contractors 
William F. Saffell, Phoenix, MD [IM] 

Rep. Power Tool Institute, Inc. 
Melvin J. Schiff, M J Schiff & Associates, CA [SE] 

Rep. American Water Works Association (VL 250) 
Deborah Ann Schouten, 3M Co., MN [U] 

Rep. Chemical Manufacturers Association 
Gregory J. Steinman, Thomas & Betts Corp., TN [M] 

Rep. National Electrical Manufacturers Association 
Ronald J. Toomer, Toomer Electrical Co. Inc., LA [DVI] 

Rep. National Electrical Contractors Association 
C. Douglas White, Houston Lighting & Power Co., TX [UT] 

Rep. Edison Electric Institute 



Alternates 



Paul M. Bowers, City of Iowa City, IA [E] 

(Alt. to J. P. Simmons) 
Paul Dobrowsky, Eastman Kodak Co., NY [U] 

(Alt. to D. A; Schouten) 
Garfield B. Gwyn, Gwyn Electrical & Plumbing Co., NC [IM] 

(Alt. to T G. Robertson) 
Ronald Lai, Framatone Connectors, NH [M] 

(Alt. to G. J. Steinman) 
Dennis E. Lammert, Union Electric Co., MO [UT] 

. (Alt. to C. D. White) 
Chiu F. Leung, Bell Communications Research (Bellcore), NJ [UT] 

(Alt. to J. Boksiner) 
Daleep C. Mohla, Union Carbide Corp., TX [U] 

(Alt. to E. Rappaport) 
David Peot, Ryobi, SC [M] 

(Alt. to W F. Saffell) 
Elliot Rush, IBEW Local 231, I A [L] 

(Alt. to D. Hammel) 

Nonvoting 
Norman H. Davis, III, Holmes Beach, FL 



CODE-MAKING PANEL NO. 6 

Articles 310, 400, 402, Chapter 9 Tables 5 through 9, 
and Appendix B 

Stephen J. Thorwegen, Jr., Chair [IM] 

Fisk Electric Co., TX 

Rep. National Electrical Contractors Association 



David Brender, Copper Development Association,' Inc., NY [M] 

Rep. Copper Development Association Inc. 
Julian R. Burns, Burns Electrical Contractors, Inc., NC [IM] 

Rep. Independent Electrical Contractors 
Kermit B. Duncan, PacifiCorp, WY [UT] 

Rep. Edison Electric Institute 
William C. Ferrell, IBEW, Local 972, OH [L] 

Rep. Int'l Brotherhood of Electrical Workers 
Steven Galan, Underwriters Laboratories Inc., NY [RT] 
Ravindra H. Ganatra, Alcan Cable, GA [M] 

Rep. The Aluminum Association 
L. Bruce McClung, Union Carbide Corp., WV [U] 

Rep. Institute of Electrical & Electronics Engineers, Inc. 
Oran P. Post, City of Cuyahoga Falls, OH [E] 

Rep. Int'l Association of Electrical Inspectors 



Alternates 



Kenneth L. Brotherton, IBEW, Local 683, OH [L] 

(Alt. to W. C. Ferrell) 
Stanley Folz, Folz Electric, Inc., IL [IM] 

(Alt. to S. J. Thorwegen, Jr.) 
G. W. "Jerry" Kent, Kent Electric Systems, TX [IM] 

(Alt. to J. R. Burns) 
C. David Mercier, Southwire Co., GA [M] 

(Alt. to R. H. Ganatra) 
Robert E. Moore, Tampa Electric Co., FL [UT] 

(Alt. to K. B. Duncan) 
Larry W. Oden, Coleman Cable Systems, Inc., IL [M] 

(Voting Alt. to NEMA Rep.) 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-10 



NATIONAL ELECTRICAL CODE COMMITTEE 



John Stacey, City of St. Louis, MO [E] 

(Alt. to O. P. Post) 
H. R. Stewart, HRS Consulting, TX [U] 

(Alt. to L. B. McClung) 



Francis M. Stone, Jr., Shell Deepwater Development Systems, Inc. 
LA [U] 
(Voting Alt. to CMA Rep.) 



CODE-MAKING PANEL NO. 7 

Articles 320, 321, 324, 325, 326, 328, 330, 333, 334, 
336, 338, 339, 340, 342, 363 

Joel A. Rencsok, Chair [E] 

City of Phoenix, AZ 

Rep. Int'l Association of Electrical Inspectors 



James M. Daly, BICC Cables Corp., NY [M] 

Rep. National Electrical Manufacturers Association 
Robert J. Eugene, City of Spokane, WA [E] 

Rep. Int'l Conference of Building Officials 
Pedro M. Garcia, Florida Power & Light Co., FL [UT] 

Rep. Edison Electric Institute 
Bobby C. Gentry, Southwire Co., GA [M] 

Rep. The Aluminum Association 
Robert L. Gotham, Rose City Electric Co., Inc., OR [IM] 

Rep. National Electrical Contractors Association 
Thomas J. Guida, Underwriters Laboratories Inc., NY [RT] • 
Ralph L. Haynes, Fluor Daniel Inc., TX [U] 

Rep. Institute of Electrical & Electronics Engineers, Inc. 
John E. Propst, Shell Oil Products, Co., TX [U] 

Rep. Chemical Manufacturers Association 
Thomas G. Rodgers, City of Daytona Beach, FL [L] 

Rep. Int'l Brotherhood of Electrical Workers 
David E. Schumacher, Schumacher Electric Co. Inc., IA [IM] 

Rep. Associated Builders and Contractors, Inc. 
Robert S. Strength, Product Safety Management Inc., FL [M] 

Rep. Society of the Plastics Industry Inc. 



Alternates 



Harry C. Brown, IBEW Local 606, FL [L] 

(Alt. to T. G. Rodgers) 
Arthur Buxbaum, San Diego Building Inspection Dept., CA [E] 

(Alt. to J. E. Rencsok) 
James V. Fitzgerald, The Okonite Co., NJ [M] 

(Alt. to J. M. Daly) 
Ravindra H. Ganatra, Alcan Cable, GA [M] 

(Alt. to B. C. Gentry) 
M. Shan Griffith, Brown & Root, Inc., TX [U] 

(Alt. to R. L. Haynes) 
Herman J. Hall, Austin, TX [M] 

(Alt. to R. S. Strength) 
Bruce W. Nutt, TU Electric, TX [UT] 

(Alt. to P. M. Garcia) 
Thomas H. Wood, Cecil B. Wood Inc., IL [IM] 

(Alt. to R. L. Gotham) 



CODE-MAKING PANEL NO. 8 

Articles 318, 331, 343, 345, 346, 347, 348, 349, 350, 351, 
352, 353, 354, 356, 358, 362, 364, 365, 374, 
Chapter 9 Tables 1 and 4, and Appendix C 

Kenneth E. Jannot, Chair [UT] 

Detroit Edison, MI 

Rep. Edison Electric Institute 



Richard Berman, Underwriters Laboratories Inc., IL [RT] 
John S. Corry, Corry Electric Inc., CA [IM] 

Rep. Associated Builders and Contractors, Inc. 
Robert W. Cox, Zeneca Pharmaceuticals Group, DE [U] 

Rep. Chemical Manufacturers Association 
George R. Dauberger, Thomas & Betts Corporation, TN [M] 

Rep. National Electrical Manufacturers Association 
Charles W. Forsberg, Carlon Electrical Products, A Lamson & Sessions 

Co., OH [M] 

Rep. SPI/VI 
Wayne A. Lilly, City of Harrisonburg, VA [E] 

Rep. Int'l Association of Electrical Inspectors 
W. Terry Lindsay, Duncan Electric Co. Inc., TN [IM] 

Rep. National Electrical Contractors Association 
Richard E. Loyd, R & N Associates, AR [M] 

Rep. American Iron and Steel Institute 
C. David Mercier, Southwire Co., GA [M] 

Rep. The Aluminum Association 
Dennis L. Rowe, The New York Board of Fire Underwriters, NY [E] 

Rep. New York Board of Fire Underwriters 
James E. Tyson, Jr., U.S. Dept. of Veterans Affairs, Washington, DC [U] 
William Wusinich, IBEW Local 98, PA [L] 

Rep. Int'l Brotherhood of Electrical Workers 



Alternates 



Kenneth E. Christ, Solutie, Inc., MO [U] 

(Alt. to R. W. Cox) 
Khimchand H. Chudasama, U.S. Dept. of Veterans Affairs, Washington, 

DC [U] 

(Alt. to J. E. Tyson, Jr.) 
Shari L. Duzac, Underwriters Laboratories Inc., CA [RT] 

(Alt. to R. Berman) 
Jack A. Gruber, Wheatland Tube Co., PA [M] 

(Alt. to R. E. Loyd) 
Wyman H. Hawley, Athens-Clarke County Government, GA [E] 

(Alt. to W. A. Lilly) 
David H. Kendall, Carlon Electrical Products, A Lamson & Sessions Co., 

OH [M] 

(Alt. to C. W. Forsberg) 
Danny P. Liggett, E. I. DuPont deNemours, DE [M] 

(Voting Alt. to CTI Rep.) 
Gilbert McGoldrick, Square D Company, OH [M] 

(Alt. to G. R. Dauberger) 
. Ray R. Simpson, Int'l Brotherhood of Electrical Workers, IN [L] 

(Alt. to W. Wusinich) 
Ronald J. Toomer, Toomer Electrical Co. Inc., LA [IM] 

(Alt. to W. T. Lindsay) - 



1999 Edition 



NATIONAL ELECTRICAL CODE 



NATIONAL ELECTRICAL CODE COMMITTEE 



70-11 



t 



CODE-MAKING PANEL NO. 9 
Articles 370, 373, 380, 384 

Timothy M. Croushore, Chair [UT] 

Allegheny Power Service Corp., PA 

Rep. Edison Electric Institute 



Joseph A. Cannatelli, Arco Chemical Co., PA [U] 

Rep. Chemical Manufacturers Association 
Dale R. Deming, Am Electric Co. (T&B), MI [M] 
Frederic P. Hartwell, Electrical Construction & Maintenance Magazine, 

MA [SE] 
Jeffrey H. Hidaka, Underwriters Laboratories Inc., IL [RT] 
Robert Kaemmerlen, Kaemmerlen Electric Co., MO [IM] 

Rep. National Electrical Contractors Association 
Anthony Montuori, The New York Board of Fire Underwriters, NY [E] 

Rep. Int'l Association of Electrical Inspectors 
Sukanta Sengupta, FMC Corp., NJ [U] 

Rep. Institute of Electrical & Electronics Engineers, Inc. 
William E. Slater, RACO Inc., IN [M] 

Rep. National Electrical Manufacturers Association 
Paul Welnak, IBEW Local 494, WI [L] 

Rep. Int'l Brotherhood of Electrical Workers 



Alternates 



Jeff Bernson, IBEW, IL [L] 

(Alt. to P. Welnak) 
Boyd H. Culp, Phillips Petroleum Co., OK [U] 

(Alt. to J. A. Cannatelli) 
Robert A. McCullough, Ocean County Construction Inspection DepL 

NJ [E] 

(Alt. to A. Montuori) 
Ronald H. Reed, Square D Company, KY [MJ 

(Alt. to W. E. Slater) 
Jerome W. Seigel, West Hartford, CT [U] 

(Alt. to S. Sengupta) 
Ronald L. Spees, Consumers Energy Co., MI [UT] 

(Alt. to T. M. Croushore) 



CODE-MAKING PANEL NO. 10 

Articles 240, 780 

Stanley D. Kahn, Chair [IM] 

Heckler Electric Co., Inc., CA 

Rep. National Electrical Contractors Association 



Charles K. Blizard, American Electrical Testing Co., Inc., MA [IM] 

Rep. Int'l Electrical Testing Association Inc. 
Madeline Borthick, May field Electric Co., TX [IM] 

Rep. Independent Electrical Contractors 
John E. Brezan, Lehigh Valley Electrical Inspection Service, PA [E] 

Rep. Int'l Association of Electrical Inspectors 
Robert J. Deaton, Union Carbide Corp., TX [U] 

Rep. Institute of Electrical & Electronics Engineers, Inc. 
Charles K. Eldridge, Indianapolis Power & Light Co., IN [UT] 

Rep. Edison Electric Institute 
Carl J. Fredericks, Dow Chemical U.S.A., TX [U] 

Rep. Chemical Manufacturers Association 
Glenn Hanson, IBEW Local 242, MN [L] 

Rep. Int'l Brotherhood of Electrical Workers 
Clive W. Kimblin, Cutler-Hammer, Inc., PA [M] 

Rep. National Electrical Manufacturers Association 
John J. Mahal, Underwriters Laboratories Inc., IL [RT] 
Arden L. Munson, Hussmann Corp., MO [M] 

Rep. Air Conditioning and Refrigeration Institute 
George J. Ockuly, Cooper Industries, Bussmann Division, MO [M] 

Alternates 

David E. Chartrand, Middle Dept. Inspection Agency, Inc., NY [E] 
(Alt. to J. E. Brezan) 



George D. Gregory, Square D Co., IA [M] 

(Alt. to C. W. Kimblin) 
Roderic L. Hageman, Prit Service, Inc., IL [IM] 

(Alt. to C. K. Blizard) 
Charles D. Hughes, Westinghouse Savannah River Co., SC [U] 

(Alt. to R. J. Deaton) 
Albert H. Keisling, IBEW Local 934, TN [L] 

(Alt. to G. Hanson) 
Allen F. KnicKrehm, The KnicKrehm Co., CA [IM] 

(Alt. to S. D. Kahn) 
Kris Mantravadi, FMC Corp., NY [U] 

(Alt. to C. J. Fredericks) 
Vincent J. Saporita, Cooper Industries, Bussmann Division, MO [M] 

(Alt. to G. J. Ockuly) 
John Tolbert, Bristol Compressors, VA [M] 

(Alt. to A. L. Munson) 
Leslie R. Zielke, South Carolina Electric and Gas Co., SC [UT] 

(Alt. to C. K. Eldridge) 

Nonvoting 
Rick C. Gilmour, Canadian Standards Association, ON, Canada 



CODE-MAKING PANEL NO. 11 

Articles 430, 440, 670, Appendix D Example D8 

Thomas H. Wood, Chair [IM] 

Cecil B. Wood Inc., IL 

Rep. National Electrical Contractors Association 



Rick L. Bunch, Tecumseh Products Co., MI [M] 
Rep. Air Conditioning and Refrigeration Institute 

Thomas E. Dye, Olin Corp., TN [U] 

Rep. Chemical Manufacturers Association 

William T. Fiske, ITS North America, NY [RT] 

Thomas J. Garvey, State of Wisconsin, WI [E] 
Rep. Int'l Association of Electrical Inspectors 



Paul S. Hamer, Chevron Research & Technology Co., CA [U] 

Rep. American Petroleum Institute 
Michael D. Landolfi, Landolfi Electric Co. Inc., NJ [IM] 

Rep. Associated Builders and Contractors, Inc. 
Timothy J. Mueck, Shermco Industries, Tnc, TX [IM] 

Rep. Int'l Electrical Testing Association Inc. 
Richard A. Rasmussen, Underwriters Laboratories Inc., NC [RT] 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-12 



NATIONAL ELECTRICAL CODE COMMITTEE 



Vincent J. Saporita, Cooper Industries, Bussmann Division, MO [M] 
Lynn F. Saunders, GM Worldwide Facilities Group., MI [U] 

Rep. Institute of Electrical & Electronics Engineers, Inc. 
Charles B. Schram, Wilmette, IL [SE] 
Thomas Sportini, IBEW Local 488, CT [L] 

Rep. Int'l Brotherhood of Electrical Workers 
M. Edward Thomas, Alabama Power Co., AL [UT] 

Rep. Edison Electric Institute 
David W. Trudeau, Factory Mutual Research, MA [I] 
James R. Wright, Siemens-Furnas Controls, IL [M] 

Rep. National Electrical Manufacturers Association 

Alternates 

Frederick Bried, Shell Oil Products Co., TX [U] 

(Alt. to P. S. Hamer) 
Joe David Cox, Eastman Chemical Co., TN [U] 

(Alt. to T. E. Dye) 



Robert J. Keough, U.S. Electrical Motors, MO [M] 

(Alt. to J. R. Wright) 
R. Ken Murphy, Houston Lighting & Power Co., TX [UT] 

(Alt. to M. E. Thomas) 
James M. Naughton, IBEW, Local 103, MA [L] 

(Alt to T. Sportini) 
George J. Ockuly, Cooper Industries, Bussmann Division, MO [M] 

(Alt. to V. J. Saporita) 
Carl Radcliffe, Underwriters Laboratories Inc., NC [RT] 

(Alt. to R. A. Rasmussen) 
John A. Schultz, Minnesota Board of Electricity, MN [EJ 

(Alt. to T. J. Garvey) 
Arthur J. Smith, III, Waldemar S. Nelson and Co., Inc., LA [U] 

(Alt. to L. F. Saunders) 
Herbert P. Spiegel, Corona Industrial Electric, CA [IM] 

(Alt. to T. H. Wood) 



CODE-MAKING PANEL NO. 12 

Articles 426, 427, 610, 620, 625, 630, 645, 660, 665, 668, 
669, 685, Appendix D Examples D9 and D10 

Charles M. Trout, Chair [IM] 

Main Electric Co. Inc., FL 

Rep. National Electrical Contractors Association 



Thomas M. Burke, Underwriters Laboratories Inc., CA [RT] 
Andre R. Cartal, Middle Dept. Inspection Agency Inc., PA [E] 

Rep. Int'l Association of Electrical Inspectors 
James F. Cook, Eagle Electric Manufacturing, NY [M] 

Rep. National Electrical Manufacturers Association 
Ralph E. Droste, United Technologies/Otis Elevator Co., CT [M] 

Rep. National Elevator Industry Inc. (VL 610, 620, 630) 
Robert A. Jones, Independent Electrical Contractors, TX [IM] 

Rep. Independent Electrical Contractors 
William J. Kelly, Eastman Kodak Co., NY [U] 

Rep. Institute of Electrical & Electronics Engineers, Inc. 
Gary M. Maurice, IBEW, Local 342, NC [L] 

Rep. Int'l Brotherhood of Electrical Workers 
John H. Mortimer, Inductotherm Corp., NJ [M] (VL 665) 
C. L. Pittman, Maryville, TN [M] 

Rep. The Aluminum Association (VL 427, 610, 625, 630, 645, 646, 

660, 665, 668, 669, 685) 
Norbert Poch, IBM Corp., MN [U] 

Rep. Information Technology Industry Council (VL 645) 
Ronald L. Purvis, Georgia Power Co., GA [UT] 

Rep. Edison Electric Institute 
S. L. Ralston, PPG Industries Inc., WV [U] 

Rep. Chemical Manufacturers Association 
Robert H. Reiiss, Material Handling, LLC, WI [M] 

Rep. Crane Manufacturers Association of America Inc. (VL 610) 
T. Neil Thorla, Inland Steel Co., IN [U] 

Rep. Association of Iron & Steel Engineers (VL 610, 620, 630) 
Craig B. Toepfer, Ford Motor Co., MI [U] 

Rep. Society of Automotive Engineers (VL 625) 
Bernard W. Whittington, Whittington Engr. Inc., WV [SE] 



Alternates 



Scott Cline, McMurtrey Electric, Inc., CA [IM] 

(Alt. to C. M. Trout) 
J. Kevin Curtis, Virginia Power, VA [UT] 

(Alt. to R. L. Purvis) 
Gary L. Duggan, IBEW Local 270, TN [L] 

(Alt. to G. M. Maurice) 
George W. Farrell, POWR-GARD Products Group, IL [M] 

(Alt. to J. F. Cook) 
Robert E. Johnson, Motorola ISG, MA [U] 

(Alt. to N. Poch) (VL 645) 
Mark G. Kosowski, General Motors Advanced Technology, MI [U] 

(Alt. to C. B. Toepfer) (VL 625) 
John R. Kovacik, Underwriters Laboratories Inc., IL [RT] 

(Alt. to T. M. Burke) 
Richard H. Laney, Siecor Corp., NC [U] 

(Voting Alt. to Insulated Cable Engineers Association Inc.) 
Nick Marchitto, Otis Elevator Co., CT [M] 

(Alt. to R. E. Droste) (VL 610, 620, 630) 
Robert C. Oldham, Jr., Reynolds Metals Co., VA [M] 

(Alt. to C. L. Pittman) (VL 427, 610, 625, 630, 645, 646, 660, 665, 

668, 669, 685) 
Merritt D. Redick, M. Redick & Associates, CA [U] 

(Alt. to W. J. Kelly) 
James J. Rogers, Massachusetts St. Board of Electrical Examiners, MA 

[E] 

(Alt. to A. R. Cartal) 
Robert C. Turner, Inductotherm Corp., NJ [M] 

(Alt. to J. H. Mortimer) (VL 665) 



CODE-MAKING PANEL NO. 13 

Articles 450, 455, 460, 470, 490 

William TV O'Grady, Chair [RT] 
Underwriters Laboratories Inc., NY 



William A. Brunner, IBEW, Local 714, ND [L] 

Rep. Int'l Brotherhood of Electrical Workers 
Hugh D. Butler, Jr., Southwire, GA [M] 

Rep. The Aluminum Association 
James C. Carroll, Square D. Co., TN [M] 

Rep. National Electrical Manufacturers Association 
William B. Crist, Houston Stafford Electric Co., TX [IM] 

Rep. Independent Electrical Contractors 



O. L. Davis, Manzano Western, Inc., NM [IM] 

Rep. National Electrical Contractors Association 
Richard P. Fogarty, Jr., Consolidated Edison Co. of N.Y., Inc., NY [UT] 

Rep. Edison Electric Institute 
Walter Kroboth, Exxon Chemical Co., TX [U] 

Rep. Chemical Manufacturers Association 
Hiram J. Lamb, City of Charlottesville, VA [E] 

Rep. Int'l Association of Electrical Inspectors 



• 



1999 Edition 



NATIONAL ELECTRICAL CODE 



NATIONAL ELECTRICAL CODE COMMITTEE 



70-13 



Milton D. Robinson, Milt Robinson Engineering Co., IN [U] 
Rep. Institute of Electrical & Electronics Engineers, Inc. 

LaVerne E. Stetson, U.S. Dept. of Agriculture, NE [SE] 
Rep. American Society of Agricultural Engineers 

Alternates 

J. Alan Barringer, North Carolina Dept. of Insurance, NC [E] 

(Alt. to H. J. Lamb) 
Jeffrey H. Hidaka, Underwriters Laboratories Inc., IL [RT] 

(Alt. to W. T. O' Grady) 
Barry N. Hornberger, PECO Energy Co., PA [UT] 

(Alt. to R. P. Fogarty, Jr.) 



Gene Morehart, ACME Electric Corp., NC [M] 

(Alt to J. C. Carroll) 
Robert L. Simpson, Simpson Electrical Engineering Co., MO [U] 

(Alt. to M. D. Robinson) 
Samuel Solomon, Alameda County Electrical JATC, CA [L] 

(Alt. to W. A. Brunner) 
Lou G. Willoughby, Aluminum Company of America, OH [M] 

(Alt. to H. D. Butler, Jr.) 
Ivan L. Winsett, Ronk Electrical Industries, GA [SE] 

(Alt. to L. E. Stetson) 
Ralph H. Young, Eastman Chemical Co., TN [U] 

(Alt. to W. Kroboth) 



CODE-MAKING PANEL NO. 14 

Articles 500, 501, 502, 503, 504, 505, 510, 511, 513, 514, 515, 516 

James G. Stallcup, Acting Chair, [SE] 
GRAYBOY & Associates, TX 



David N. Bishop, Chevron U.S.A. Production Co., TX [U] 

Rep. American Petroleum Institute 
Edward M. Briesch, Underwriters Laboratories Inc., IL [RT] 
Donald R. Cook, Shelby County Bldg. Inspections, AL [E] 

Rep. Int'l Association of Electrical Inspectors 
James D. Cospolich, Waldemar S. Nelson & Co. Inc., LA [U] 

Rep. Int'l Society for Measurement and Control 
Kevin P. Earley, Bay Harbour Electric, Inc., PA [IM] 

Rep. Independent Electrical Contractors 
Joseph H. Kuczka, Killark Electric Mfg. Co., MO [M] 

Rep. National Electrical Manufacturers Association 
Francis J. McGowan, Factory Mutual Research Corp., MA [I] 
Carl R. Roselli, ANR Pipeline Co., MI [U] 

Rep. American Gas Association 
Mark G. Saban, Modern Electric Co. of Illinois, IL [IM] 

Rep. National Electrical Contractors Association 
Peter J. Schram, Delray Beach, FL [SE] 
Harold B. Smith, Wunderlich-Malec Eng., MN [U] 

Rep. Grain Elevator & Processing Society 
Lawrence C. Strachota, Mid American Energy Co., IA [UT] 

Rep. Edison Electric Institute 
David Wechsler, Union Carbide Corp., WV [U] 

Rep. Chemical Manufacturers Association 
James A. Weldon, IBEW Local 728, FL [L] 

Rep. Int'l Brotherhood of Electrical Workers 
Donald W. Zipse, Zipse Electrical Engineering Inc., PA [U] 

Rep. Institute of Electrical & Electronics Engineers, Inc. 



Alternates 

Lawrence J. Adamcik, The Dow Chemical Co., MI [U] 

(Alt. to D. W. Zipse) 
Alonza W. Ballard, Crouse-Hinds, NY [M] 

(Alt. to J. H. Kuczka) 
Jimmy R. Bonds, Oklahoma State Dept. of Health, OK [E] 

(Alt. to D. R. Cook) 
Keith E. Feigel, IBEW Local 180, CA [L] 

(Alt. to J. A. Weldon) 
Mark Goodman, ARCO Products Co, CA [U] 

(Alt. to D. N. Bishop) 
Paul T. Kelly, Underwriters Laboratories Inc., IL [RT] 

(Alt. to E. M. Briesch) 
William G. Lawrence, Jr., Factory Mutual Research Corp., MA [I] 

(Alt. to F. J. McGowan) 
Richard A. Pruzick, PC Electrical Construction, Inc., NJ [IM] 

(Alt. to M. G. Saban) 
William R. Stalker, ComEd Division of Unicom, IL [LIT] 

(Alt. to L. C. Strachota) 
Mark C. Wirfs, R & W Engineering Inc., OR [U] 

(Alt. to H. B. Smith) 

Nonvoting 

John A. Bossert, Hazloc Inc., ON, Canada 
Fred K. Walker, U.S. Air Force, FL 



CODE-MAKING PANEL NO. 15 

Articles 445, 480, 518, 520, 525, 530, 540, 695, 700, 701, 702, 705 

Robert C. Duncan, Chair [E] 

Reedy Creek Improvement District, FL 

Rep. Int'l Association of Electrical Inspectors 



Peter W. Amos, Consolidated Edison Co. of NY, Inc., NY [UT] 

Rep. Edison Electric Institute 
Lloyd D. Bird Jr., Belco Electric, Inc., GA [IM] 

Rep. Independent Electrical Contractors 
James L. Boyer, Firetrol, Inc., NC [M] 

Rep. Nat'l Electrical Manufacturers Association 
Tom Dunn, Butler Amusements, CA [IM] 

Rep. Outdoor Amusement Business Association, Inc. (VL 525) 
George W. Flach, Flach Consultants, LA [SE] 
Michael V. Glenn, Longview Fibre Co., WA [U] 

Rep. Institute of Electrical & Electronics Engineers, Inc. 
Marcelo M. Hirschler, GBH Int'l, CA [SE] 
George Thomas Howard, George Thomas Howard & 
Associates, NV [SE] 
Gordon S. Johnson, Dundee, FL [SE] 

Rep. Electrical Generating Systems Association 
Jack W. Kalbfeld, Kalico Technology Inc., NY [SE] (VL 518, 520, 525, 

530, 540) 



Michael B. Klein, Labyrinth Electrical, Inc., MD [IM] 

Rep. Illuminating Engineering Society of North America 
John R. Kovacik, Underwriters Laboratories Inc., IL [RT] 
Edwin S. Kramer, Radio City Music Hall, NY [L] 

Rep. Int'l Association of Theatrical Stage Employees 
Michael A. Lanni, Universal City Studios, CA [U] 

Rep. Motion Picture Association of America, Inc. 
Stephen A. Mezsick, Eli Lilly & Co., IN [U] 

Rep. Chemical Manufacturers Association 
Keku M. Mistry, Bell Communications Research (Bellcore), NJ [UT] 

Rep. Alliance for Telecommunications Industry Solutions (VL 445, 

480, 700, 701, 702, 705) 
Richard M. Shotwell, Filer, ID [IM] 
Rep. National Electrical Contractors Association 
Lawrence E. Todd, Intertek Testing Services, NA, Inc. KY [RT] 
Kenneth E. Vannice, NSI Corp., OR [M] 

Rep. U.S. Institute for Theatre Technology 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-14 



NATIONAL ELECTRICAL CODE COMMITTEE 



Alternates 

James T. Dollard, Jr., IBEW Local 98, PA [L] 

(Voting Alt. to IBEW Rep.) 
Mitchell K. Hefter, Rosco Entertainment Technology, OR [IM] 

(Alt. to M. B. Klein) 
James R. Iverson, Onan Corp., MN [M] 

(Alt. to G. S. Johnson) 
Dennis W. Marshall, T.D.B., Inc., TX [IM] 

(Alt. to L. D. Bird, Jr.) 
Irvin R. Miller, American Electric Power, OH [UT] 

(Alt. to P. W. Amos) 
Ronald H. Minter, Kaufel Tech Center, CT [M] 

(Alt. to J. L. Boyer) 



Michael D. Skinner, CBS Studio Center, CA [U] 

(Alt. to M. A. Lanni) 
Richard Sobel, Quantum Electric Corp., NY [IM] 

(Alt. of R. M. Shotwell) 
Steven R. Terry, Production Arts Lighting Inc., NJ [U] 

(Alt. to K. E. Vannice) 
Dale A. Triffo, Shell Oil Products Co., TX [U] 

(Alt to. S. A. Mezsick) 
Harold F. Willman, City of Lakewood, CO [E] 

(Alt. to R. C. Duncan) 



CODE-MAKING PANEL NO. 16 

Articles 640, 650, 720, 725, 727, 760, 770, 800, 810, 820, 830, and Chapter 9 

Tables 11 and 12 

Dean K. Wilson, Chair [I] 
Industrial Risk Insurers, CT 
Rep. Industrial Risk Insurers 



George J. Bagnall, Rural Utilities Service, Washington, DC [UT] 
James E. Brunssen, Bell Communications Research (Bellcore), NJ [UT] 

Rep. Alliance for Telecommunications Industry Solutions 
A. William Coaker, A. W. Coaker & Associates, Inc., OH [M] 

Rep. Society of the Plastics Industry Inc. 
Gerald Lee Dorna, Belden Wire & Cable, IN [M] 

Rep. Insulated Cable Engineers Association Inc. 
S. E. Egesdal, Honeywell Inc., MN [M] 

Rep. National Electrical Manufacturers Association 
C. Jeff Goins, Quarry Electric, Inc., FL [IM] 

Rep. Independent Electrical Contractors 
Lee C. Hewitt, Underwriters Laboratories Inc., IL [RT] 
Steven C. Johnson, Time Warner Cable, CO [IM] 

Rep. National Cable Television Association 
Ronald G. Jones, Ronald G. Jones, PE, TX [U] 

Rep. Institute of Electrical & Electronics Engineers, Inc. 
Harry F. Katz, South Texas Electrical JATC, TX [L] 

Rep. Int'l Brotherhood of Electrical Workers 
Stanley Kaufman, Lucent Technologies, GA [M] 
Michael A. Lanni, Universal City Studios, CA [U] 

Rep. Motion Picture Association of America, Inc. (VL 640, 720, 725, 

760, 810, 820) 
John Mangan, Medford City Hall, MA [E] 

Rep. Int'l Association of Electrical Inspectors 
Michael E. McNeil, FMC Corp/Food Ingredients 

Division, ME [U] 

Rep. Chemical Manufacturers Association 
W. D. Pirkle, Pirkle Electric Co., Inc., GA [IM] 

Rep. National Electrical Contractors Association 
James W. Romlein, MIS Labs, WI [M] 

Rep. Building Industry Consulting 'Service Int'l 
Kyle E. Todd, Entergy - GSU, LA [UT] 

Rep. Edison Electric Institute 
Inder L. Wadehra, IBM Corp., NC [U] 

Rep. Information Technology Industry Council 



Melvin J. Wierenga, Wierenga & Associates, MI [TM] 

Rep. National Systems Contractors Association/Consumer 
Electronics Manufacturers Association 

Alternates 

Ronald P. Cantrell, IBEW Local 72, TX [L] 

(Alt. to H. F. Katz) 
Chrysanthos Chrysaanthou, Bell Communications Research (Bellcore), 

NJ [UT] 

(Alt. to J. E. Brunssen) 
William Hopple, Simplex Time Recorder Co., CA [M] 

(Alt. to S. E. Egesdal) 
Robert Jensen, Telecommunication Infrastructure Design, TX [M] 

(Alt. to J. W. Romlein) 
Ray A. Jones, The DuPont Company, DE [U] 

(Alt. to M. E. McNeil) 
William J. McCoy, GTE Telephone Operations, TX [U] 

(Alt. to R. G. Jones) 
Andy W. Mobley, 3M, MN [U] 

(Voting Alt. to ISA Rep.) 
Joseph W. Rao, RAO Electric Co., FL [IM] 

(Alt. to C. J. Goins) 
Jan Rowland, Houston, TX [M] 

(Voting Alt. to AIOB and APOBA Rep.) (VL 640, 650, 720, 725) 
Oleh Sniezko, TCI Communications, Inc., CO [IM] 

(Alt. to S. C. Johnson) 
Sondra K. Todd, KPL a Western Resources Co., KS [UT] 

(Alt. to K. E. Todd) 
William A. Zanicchi, The New York Board of Fire Underwriters, NY [E] 

(Alt. to J. Mangan) 

Nonvoting 

Irving Mande, Edwards Systems Tech, CT 
(Member Emeritus) 



CODE-MAKING PANEL NO. 17 
Article 517 

Robert E. Bernd, Chair [RT] 
Underwriters Laboratories Inc., IL 



Stephen Benesh, Square D Co., WI [M] 

Rep. National Electrical Manufacturers Association 
Britton E. Berek, American Society for Healthcare Engineering, IL [U] 

Rep. American Society for Healthcare Engineering 
D. R. Borden, Jr., Tri-City Electric Co. Inc., FL [IM] 

Rep. National Electrical Contractors Association 
Thomas C. Clark, Clark Electrical Construction, Inc., TX [IM] 

Rep. Associated Builders and Contractors, Inc. 



James R. Duncan, Sparling, WA [U] 

Rep. Institute of Electrical & Electronics Engineers, Inc. 
Thomas H. Gilliam, Riverside Methodist Hospital, OH [U] 

Rep. Association for the Advancement of Medical 

Instrumentation 
James A. Meyer, Pettis Memorial VA Hospital, CA [C] 

Rep. American Society of Anesthesiologists 
Hugh O. Nash, Jr., Nash Lipsey Burch, LLC, TN [SE] 



1999 Edition 



NATIONAL ELECTRICAL CODE 



NATIONAL ELECTRICAL CODE COMMITTEE 



70-15 



J. Randal] Perdue, Entergy Services Inc., AR [UT] 

Rep. Edison Electric Institute 
Jim M. Schmer, Boise City Building Dept., ID [E] 

. Rep. Int'l Association of Electrical Inspectors 
George Schuck, Jr., IBEW Local 3, NY [L] 

Rep. Int'l Brotherhood of Electrical Workers 
Jeffrey L. Steplowski, U.S. Dept. of Veterans Affairs, Washington, DC 

[U] 
Duane J. Telecky, Washoe Medical Center, NV [U] 

Rep. NFPA Health Care Section . 
Mike Velvikis, High Voltage Maintenance Corp., WI [IM] 

Rep. Int'l Electrical Testing Association Inc. 
Walter N. Vernon, IV, Mazzetti & Associates, Inc., CA [SE] 

Rep. Consulting Engineers & Land Surveyors of CA 

Alternates 

Steve Campolo, Leviton Mfg. Co., Inc., NY [M] 
(Alt. to S. Benesh) 



Matthew B. Dozier, Smith Seckman Reid, Inc., TN [U] 

(Alt. to J: R. Duncan) 
Stephen D. Hewson, Underwriters Laboratories Inc., IL [RT] 

(Alt. to R. E. Bernd) 
Stanley D. Kahn, Heckler Electric Co., Inc., CA [IM] 

(Alt. to D. R. Borden, Jr.) 
Thomas L. Ryder, IBEW Local 692, MI [L] 

(Alt. to G. Schuck, Jr.) 
Gary D. Slack, Healthcare Engineering Consultants, OH [U] 

(Alt. to B. E. Berek) 
Richard H. Smith, OG&E Electric Services, OK [UT] 

(Alt. to J. R. Perdue) 
James E. Tyson, Jr., U.S. Dept. of Veterans Affairs, Washington, DC [U] 

(Alt. to J. L. Steplowski) 



CODE-MAKING PANEL NO. 18 

Articles 410, 411, 600, 605 

Wayne Brinkmeyer, Chair [IM] 

Biddle Electric Corp., TX 

Rep. National Electrical Contractors Association 



Rudy T. Elam, Systems Engineering Services, TN [U] 

Rep. Institute of Electrical & Electronics Engineers, Inc. 
Kenneth F. Kempel, Underwriters Laboratories Inc., NC [RT] 
Thomas J. Lynch, IBEW Local 99, RI [L] 

Rep. Int'l Brotherhood of Electrical Workers 
Bernard J. Mezger, American Lighting Association, MA [M] 

Rep. American Lighting Association (VL 410, 411) 
James F. Pierce, Intertek Testing Services NA Inc., OR [RT] 
Saul Rosenbaum, Leviton Mfg. Co. Inc., NY [M] 

Rep. National Electrical Manufacturers Association 
Thomas E. Trainor, City of San Diego, CA [E] 

Rep. Int'l Association of Electrical Inspectors 
Carl T. Wall, Alabama Power Co., AL [UT] 

Rep. Edison Electric Institute 
Jack Wells, Pass & Seymour Legrand, NY [M] 
David B. Wilson, Southwest Signs, TX [IM] 

Rep. Independent Electrical Contractors 
Randall K. Wright, Wright Sign Co., PA [M] 

Rep. Int'l Sign Association (VL 600) 



Alternates 



Michael N. Ber, IEC, Houston, TX [IM] 

(Alt. to D. B. Wilson) 
Mark R. Berner, PP&L, PA [UT] 

(Alt. to C. T. Wall) 
Robert L. Cochran, City of Costa Mesa, CA [E] 

(Alt. to T. E. Trainor) 
Howard D. Hughes, Hughes Electric Co. Inc., AR [IM] 

(Alt. to W. Brinkmeyer) 
Stephen G. Kieffer, Kieffer & Co., Inc., WI [M] 

(Alt. to R. K. Wright) (VL 600) 
Steven A. Larson, Lockhead Martin Energy Systems, TN [U] 

(Alt. to R. T. Elam) 
Don Miletich, Cooper Lighting, IL [M] 

(Alt. to S. Rosenbaum) 
Michael S. O'Boyle, Lightolier, Inc., MA [M] 

(Alt. to B. J. Mezger) (VL 410, 411) 
David O. Thomas, IBEW Local 208, CT [L] 

(Alt. to T J. Lynch) 



CODE-MAKING PANEL NO. 19 

Articles 545, 547, 550, 551, 552, 553, 555, 604, 675 

Robert A. McCullough, Chair [E] 

Ocean County Construction Inspection Dept., NJ 

Rep. Int'l Association of Electrical Inspectors 



Barry Bauman, Wisconsin Power & Light Co., WI [UT] 

Rep. American Society of Agricultural Engineers (VL 545, 547, 604, 

675) 
William C. Boteler, Hubbell Inc., CT [M] 

Rep. National Electrical Manufacturers Association 
James W. Finch, Kampgrounds of America, Inc., MT [U] (VL 550, 551, 

552, 555) 
Bruce A. Hopkins, Recreation Vehicle Industry 
Association, VA [M] (VL 550, 551, 552) 
Robert L. LaRocca, Underwriters Laboratories Inc., NY [RT] 
Thomas J. LeMay, LeMay Electric, Inc., GA [IM] 

Rep. Independent Electrical Contractors 
Tug Miller, California Travel Parks Association, CA [U] 

Rep. National Assn. of RV Parks & Campgrounds (VL 550, 551, 552) 
John "Lou" Reid, IBEW Local 595, CA [L] 

Rep. Int'l Brotherhood of Electrical Workers 
Leslie Sabin-Mercado, San Diego Gas & Electric Co., CA [UT] 

Rep. Edison Electric Institute 



Dick Veenstra, Fleetwood Enterprises, Inc., CA [M] 

Rep. Manufactured Housing Institute (VL 550, 551, 552) 

Paul Wahlstrom, Ahlstrom Schaeffer Electric Corp., NY [IM] 
Rep. National Electrical Contractors Association 

Michael L. Zieman, RADCO, CA [RT] (VL 545, 550, 551, 552) 

Alternates 

Glenn H. Ankenbrand, Delmarva Power, MD [UT] 

(Alt. to L. Sabin-Mercado) 
David Gorin, National Assn. of RV Parks & 
Campgrounds, VA [U] 

(Alt. to T. Miller) (VL 550, 551, 552) 
Ronald E. Maassen, Lemberg Electric Co., Inc., WI [IM] 

(Alt. to P. Wahlstrom) 
Neal Mahan, Underwriters Laboratories Inc., NC [RT] 

(Alt. to R. L. LaRocca) 
Timothy P. McNeive, Thomas & Betts Corp., TN [M] 

(Alt. to W. C. Boteler) 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-16 



NATIONAL ELECTRICAL CODE COMMITTEE 



William A. Mirand, IBEW Local 46, WA [L] 

(Alt. to J. Reid) 
Kent Perkins, Recreation Vehicle Industry Association, VA [M] 

(Alt. to B. A. Hopkins) (VL 550, 551, 552) *'' 

John G. Sims, Champion Enterprises, MI [M] 

(Alt. to D. Veenstra) (VL 550, 551, 552) 



Homer Staves, Kampgrounds of America, Inc., MT [U] 
(Alt. to J. W. Finch) (VL 550, 551, 552, 555) 

La Verne E. Stetson, U.S. Dept. of Agriculture, NE [U] 
(Alt. to B. Bauman) (VL 545, 547, 604, 675) 

Raymond F. Tucker, RADCO, CA [RT] 

. (Alt. to M. L. Zieman) (VL 545, 550, 551, 552) 



CODE-MAKING PANEL NO. 20 

Articles 422, 424, 680 

Robert M. Milatovich, Chair [E] 

Clark County, NV 

Rep. Int'l Association of Electrical Inspectors 



Edward S. Charkey, American Insurance Services Group, Inc., NY [I] 
Robert J. Egan, IBEW Local 1, MO [L] 

Rep. Int'l Brotherhood of Electrical Workers 
James N. Pearse, Leviton Mfg. Co. Inc., NY [M] 

Rep. National Electrical Manufacturers Association 
Marcos Ramirez, Mr. Electric Service Co., Inc., NY [IM] 

Rep. Independent Electrical Contractors 
William F. Ryan, Jr., The New York Board of Fire Underwriters, NY [E] 
Herbert P. Spiegel, Corona Industrial Electric, Inc., CA [IM] 

Rep. National Electrical Contractors Association 
Donald J. Talka, Underwriters Laboratories Inc., NY [RT] 
Leon T. Uhl, Leon T. Uhl, PE, IL [M] 

Rep. Association of Home Appliance Manufacturers (VL 422, 424) 
Leonard K. VanTassel, Carrier Air Conditioning, NY [M] 

Rep. Air Conditioning and Refrigeration Institute (VL 422, 424) 
Lee L. West, Balboa Instruments, CA [M] 

Rep. National Spa and Pool Institute (VL 680) 
Robert M. Yurkanin, Electran Process Int'l Inc., NJ [U] 

Rep. Institute of Electrical & Electronics Engineers, Inc. 

Alternates 

Xen George Anchales, San Bernardino County/Dept. of Bldg. & Safety, 
CA [E] 
(Alt. to R. M. Milatovich) 



NOTE: Membership on a committee shall not in and of itself constitute an endorsement of the Association or any 
document developed by the committee on which the member serves. 

Committee Scope. This Committee shall have primary responsibility for documents on minimizing the risk of 
electricity as a source of electric shock and as a potential ignition source of fires and explosions. It shall also be 
responsible for text to minimize the propagation of fire and explosions due to electrical installations. 



Dennis L. Baker, Springs & Sons Electrical Contractors Inc., AZ [IM] 

(Alt. to M. Ramirez) 
Scott Cline, McMurtrey Electric, Inc., CA [IM] 

(Alt. to H. P. Spiegel) 
Neil F. LaBrake, Jr., Niagara Mohawk Power Corp., NY.[UT] 

(Voting Alt. to ELPG/EEI Rep.) 
Earle L. McNairn, BICC Pyrotenax, ON, Canada [M] 

(Alt. to J. N. Pearse) 
Anthony Sardina, Carrier Corp., NY [M] 

(Alt. to L. K. VanTassel) (VL 422, 424) 
Stephen P. Schoemehl, IBEW Local 1, MO [L] 

(Alt. to R. J. Egan) 
John T. Weizeorick, Assn. of Home Appliance Manufacturers, IL [M] 

(Alt. to L. T. Uhl) (VL 422, 424) 
Robert E. Wisenburg, Coates Heater Co., Inc., WA [M] 

(Alt. to L. L. West) (VL 680) 

Nonvoting 

Rick C. Gilmour, Canadian Standards Association, ON, Canada 
William H. King, Jr., U.S. Consumer Product Safety Commission, MD 



1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 90 — INTRODUCTION 



70-17 



NFPA 70 

National Electrical Code^ 

1999 Edition 



Article 90 — Introduction 

90-1. Purpose. 

(a) Practical Safeguarding. The purpose of this Code is 
the practical safeguarding of persons and property from haz- 
ards arising from the use of electricity. 

(b) Adequacy. This Code contains provisions that are con- 
sidered necessary for safety. Compliance therewith and 
proper maintenance will result in an installation that is essen- 
tially free from hazard but not necessarily efficient, conve- 
nient, or adequate for good service or future expansion of 
electrical use. 

FPN: Hazards often occur because of overloading of wiring 
systems by methods or usage not in conformity with this 
Code. This occurs because initial wiring did not provide 
for increases in the use of electricity. An initial adequate 
installation and reasonable provisions for system changes 
will provide for future increases in the use of electricity. 

(c) Intention. This Code is not intended as a design speci- 
fication nor an instruction manual for untrained persons. 

90-2. Scope. 

(a) Covered. This Code covers the following. 

(1) Installations of electric conductors and equipment 
within or on public and private buildings or other structures, 
including mobile homes, recreational vehicles, and floating 
buildings; and other premises such as yards, carnival, park- 
ing, and other lots, and industrial substations. 

FPN: For additional information concerning such installa- 
tions in an industrial or multibuilding complex, see the 
National Electrical Safety Code, ANSI C2-1997. 

(2) Installations of conductors and equipment that con- 
nect to the supply of electricity. 

(3) Installations of other outside conductors and equip- 
ment on the premises. 

(4) Installations of optical fiber cables and raceways. 

(5) Installations in buildings used by the electric utility, 
such as office buildings, warehouses, garages, machine 
shops, and recreational buildings; that are not an integral 
part of a generating plant, substation, or control center. 



(b) Not Covered. This Code does not cover the following. 

(1) Installations in ships, watercraft other than floating 
buildings, railway rolling stock, aircraft, or automotive vehi- 
cles other than mobile homes and recreational vehicles. 

FPN: While the scope of this Code indicates that the Code . 
does not cover installations in ships, portions of this Code 
are incorporated by reference into Title 46, Code of Federal 
Regulations, Parts 110-113. 

(2) Installations underground in mines and self-propelled 
mobile surface mining machinery and its attendant electrical 
trailing cable. 

(3) Installations of railways for generation, transforma- 
tion, transmission, or distribution of power used exclusively 
for operation of rolling stock or installations used exclusively 
for signaling and communications purposes. 

(4) Installations of communications equipment under the 
exclusive control of communications utilities located out- 
doors or in building spaces used exclusively for such instal- 
lations. 

(5) Installations, including associated lighting, under the 
exclusive control of electric utilities for the purpose of com- 
munications, metering, generation, control, transformation, 
transmission, or distribution of electric energy. Such instal- 
lations shall be located in buildings used exclusively by 
utilities for such purposes; outdoors on property owned or 
leased by the utility; on or along public highways, streets, 
roads, etc.; or outdoors on private property by established 
rights such as easements. 

(c) Special Permission. The authority having jurisdiction 
for enforcing this Code may grant exception for the installa- 
tion of conductors and equipment that are not under the 
exclusive control of the electric utilities and are used to 
connect the electric utility supply system to the service- 
entrance conductors of the premises served, provided such 
installations are outside a building or terminate immediately 
inside a building wall. 

90-3. Code Arrangement. This Code is divided into the 
introduction and nine chapters. Chapters 1, 2, 3, and 4 apply 
generally; Chapters 5, 6, arid 7 apply to special occupancies, 
special equipment, or other special conditions. These latter 
chapters supplement or modify the general rules. Chapters 
1 through 4 apply except as amended by Chapters 5, 6, and 
7 for the particular conditions. 

Chapter 8 covers communications systems and is inde- 
pendent of the other chapters except where they are specifi- 
cally referenced therein. 

Chapter 9 consists of tables. 

Material identified by the superscript letter "x" includes 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-18 



ARTICLE 90 — INTRODUCTION 



text extracted from other National Fire Protection Associa- 
tion (NFPA) documents as identified in Appendix A. 

90-4. Enforcement. This Code is intended to be suitable 
for mandatory application by governmental bodies that exer- 
cise legal jurisdiction over electrical installations and for use 
by insurance inspectors. The authority having jurisdiction for 
enforcement of the Code will have the responsibility for 
making interpretations of the rules, for deciding on the ap- 
proval of equipment and materials, and for granting the 
special permission contemplated in a number of the rules. 

The authority having jurisdiction may waive specific re- 
quirements in this Code or permit alternate methods where 
it is assured that equivalent objectives can be achieved by 
establishing and maintaining effective safety. 

This Code may require new products, constructions, or 
materials that may not yet be available at the time the Code 
is adopted. In such event, the authority having jurisdiction 
may permit the use of the products, constructions, or materi- 
als that comply with the most recent previous edition of this 
Code adopted by the jurisdiction. 

90-5. Mandatory Rules, Permissive Rules, and Explana- 
tory Material. 

(a) Mandatory Rules. Mandatory rules of this Code are 
those that identify actions that are specifically required or 
prohibited and are characterized by the use of the terms 
shall or shall not. 

(b) Permissive Rules. Permissive rules of this Code are 
those that identify actions that are allowed but not required, 
are normally used to describe options or alternative methods, 
and are characterized by the use of the terms shall be permit- 
ted or shall not be required. 

(c) Explanatory Material. Explanatory material, such as 
references to other standards, references to related sections of 
this Code, or information related to a Code rule, is included in 
this Code in the form of fine print notes (FPN). Fine print 
notes are informational only and are not enforceable as re- 
quirements of this Code. 

FPN: The format and language used in this Code follows 
guidelines established by NFPA and published in the NEC 
Style Manual. Copies of this manual may be obtained from 
NFPA. 

90-6. Formal Interpretations. To promote uniformity of 
interpretation and application of the provisions of this Code, 
formal interpretation procedures have been established and 
are found in the NFPA Regulations Governing Committee 
Projects. 

90-7. Examination of Equipment for Safety. For specific 
items of equipment and materials referred to in this Code, 



examinations for safety made under standard conditions will 
provide a basis for approval where the record is made gener- 
ally available through promulgation by organizations prop- 
erly equipped and qualified for experimental testing, 
inspections of the run of goods at factories, and service- 
value determination through field inspections. This avoids 
the necessity for repetition of examinations by different ex- 
aminers, frequently with inadequate facilities for such work, 
and the confusion that would result from conflicting reports 
as to the suitability of devices and materials examined for 
a given purpose. 

It is the intent of this Code that factory-installed internal 
wiring or the construction of equipment need not be in- 
spected at the time of installation of the equipment, except 
to detect alterations or damage, if the equipment has been 
listed by a qualified electrical testing laboratory that is rec- 
ognized as having the facilities described above and that 
requires suitability for installation in accordance with this 
Code. 

FPN No. 1: See requirements in Section 110-3. 
FPN No. 2: Listed is defined in Article 100. 



90-8. Wiring Planning. 

(a) Future Expansion and Convenience. Plans and speci- 
fications that provide ample space in raceways, spare race- 
ways, and additional spaces will allow for future increases 
in the use of electricity. Distribution centers located in readily 
accessible locations will provide convenience and safety of 
operation. 

(b) Number of Circuits in Enclosures. It is elsewhere 
provided in this Code that the number of wires and circuits 
confined in a single enclosure be varyingly restricted. Lim- 
iting the number of circuits in a single enclosure will mini- 
mize the effects from a short circuit or ground fault in one 
circuit. 



90-9. Metric Units of Measurement. For the purpose of 
this Code, metric units of measurement are in accordance 
with the modernized metric system known as the Interna- 
tional System of Units (SI). 

Values of measurement in the Code text will be followed 
by an approximate equivalent value in SI units. Tables will 
have a footnote for SI conversion units used in the table. 

Conduit size, wire size, horsepower designation for mo- 
tors, and trade sizes that do not reflect actual measurements, 
e.g., box sizes, will not be assigned dual designation SI 
units. 



1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 100 — DEFINITIONS 



70-19 



CHAPTER 1 
General 

Article 100 — Definitions 

Scope. This article contains only those definitions essential 
to the proper application of this Code. It is not intended 
to include commonly defined general terms or commonly 
defined technical terms from related codes and standards. 
In general, only those terms that are used in two or more 
articles are defined in Article 100. Other definitions are 
included in the article in which they are used but may be 
referenced in Article 100. 

Part A of this article contains definitions intended to 
apply wherever the terms are used throughout this Code. 
Part B contains definitions applicable only to the parts of 
articles specifically covering installations and equipment 
operating at over 600 volts, nominal. 

A. General 

Accessible (as applied to wiring methods). Capable of 
being removed or exposed without damaging the building 
structure or finish, or not permanently closed in by the 
structure or finish of the building. 

Accessible (as applied to equipment). Admitting close 
approach; not guarded by locked doors, elevation, or other 
effective means. 

Accessible, Readily (Readily Accessible). Capable of 
being reached quickly for operation, renewal, or inspections, 
without requiring those to whom ready access is requisite 
to climb over or remove obstacles or to resort to portable 
ladders, etc. 

Ampacity. The current, in amperes, that a conductor can 
carry continuously under the conditions of use without ex- 
ceeding its temperature rating. 

Appliance. Utilization equipment, generally other than 
industrial, normally built in standardized sizes or types, that 
is installed or connected as a unit to perform one or more 
functions such as clothes washing, air conditioning, food 
mixing, deep frying, etc. 

Approved. Acceptable to the authority having jurisdic- 
tion. 

Askarel. A generic term for a group of nonflammable 
synthetic chlorinated hydrocarbons used as electrical insu- 
lating media. Askarels of various compositional types are 
used. Under arcing conditions, the gases produced, while 
consisting predominantly of noncombustible hydrogen chlo- 
ride, can include varying amounts of combustible gases de- 
pending on the askarel type. 



Attachment Plug (Plug Cap) (Plug). A device that, by 
insertion in a receptacle, establishes a connection between 
the conductors of the attached flexible cord and the conduc- 
tors connected permanently to the receptacle. 

Automatic. Self-acting, operating by its own mechanism 
when actuated by some impersonal influence, as, for exam- 
ple, a change in current strength, pressure, temperature, or 
mechanical configuration. 

Bathroom. An area including a basin with one or more 
of the following: a toilet, a tub, or a shower. 

Bonding (Bonded). The permanent joining of metallic 
parts to form an electrically conductive path that will ensure 
electrical continuity and the capacity to conduct safely any 
current likely to be imposed. 

Bonding Jumper. A reliable conductor to ensure the 
required electrical conductivity between metal parts required 
to be electrically connected. 

Bonding Jumper, Equipment. The connection between 
two or more portions of the equipment grounding conductor. 

Bonding Jumper, Main. The connection between the 
grounded circuit conductor and the equipment grounding 
conductor at the service. 

Branch Circuit. The circuit conductors between the 
final overcurrent device protecting the circuit and the out- 
lets). 

Branch Circuit, Appliance. A branch circuit that sup- 
plies energy to one or more outlets to which appliances are 
to be connected, and that has no permanently connected 
lighting fixtures that are not a part of an appliance. 

Branch Circuit, General Purpose. A branch circuit that 
supplies a number of outlets for lighting and appliances. 

Branch Circuit, Individual. A branch circuit that sup- 
plies only one utilization equipment. 

Branch Circuit, Multiwire. A branch circuit that con- 
sists of two or more ungrounded conductors that have a 
potential difference between them, and a grounded conductor 
that has equal potential difference between it and each un- 
grounded conductor of the circuit and that is connected to 
the neutral or grounded conductor of the system. 

Building. A structure that stands alone or that is cut off 
from adjoining structures by fire walls with all openings 
therein protected by approved fire doors. 

Cabinet. An enclosure designed either for surface 
mounting or flush mounting and is provided with a frame, 
mat, or trim in which a swinging door or doors are or can 
be hung. 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-20 



ARTICLE 100 — DEFINITIONS 



Circuit Breaker. A device designed to open and close 
a circuit by nonautomatic means and to open the circuit 
automatically on a predetermined overcurrent without dam- 
age to itself when properly applied within its rating. 

FPN: The automatic opening means can be integral, direct 
acting with the circuit breaker, or remote from the circuit 
breaker. 

Adjustable (as applied to circuit breakers). A qualifying 
term indicating that the circuit breaker can be set to trip at 
various values of current, time, or both, within a predeter- 
mined range. 

Instantaneous Trip (as applied to circuit breakers). A 
qualifying term indicating that no delay is purposely intro- 
duced in the tripping action of the circuit breaker. 

Inverse Time (as applied to circuit breakers). A qualify- 
ing term indicating that there is purposely introduced a delay 
in the tripping action of the circuit breaker, which delay 
decreases as the magnitude of the current increases. 

Nonadjustable (as applied to circuit breakers). A quali- 
fying term indicating that the circuit breaker does not have 
any adjustment to alter the value of current at which it will 
trip or the time required for its operation. 

Setting (of circuit breakers). The value of current, time, 
or both, at which an adjustable circuit breaker is set to trip. 

Concealed. Rendered inaccessible by the structure or 
finish of the building. Wires in concealed raceways are con- 
sidered concealed, even though they may become accessible 
by withdrawing them. 

Conductor. 

Bare. A conductor having no covering or electrical insu- 
lation whatsoever. 

Covered. A conductor encased within material of compo- 
sition or thickness that is not recognized by this Code as 
electrical insulation. 

Insulated. A conductor encased within material of com- 
position and thickness that is recognized by this Code as 
electrical insulation. 

Conduit Body. A separate portion of a conduit or tubing 
system that provides access through a removable cover(s) 
to the interior of the system at a junction of two or more 
sections of the system or at a terminal point of the system. 
Boxes such as FS and FD or larger cast or sheet metal 
boxes are not classified as conduit bodies. 

Connector, Pressure (Solderless). A device that estab- 
lishes a connection between two or more conductors or 
between one or more conductors and a terminal by means 
of mechanical pressure and without the use of solder. 



Continuous Load. A load where the maximum current 
is expected to continue for 3 hours or more. 

Controller. A device or group of devices that serves to 
govern, in sojne predetermined manner, the electric power 
delivered to the apparatus to which it is connected. 

Cooking Unit, Counter-Mounted. A cooking appliance 
designed for mounting in or on a counter and consisting of 
one or more heating elements, internal wiring, and built-in 
or separately mountable controls. 

Copper-Clad Aluminum Conductors. Conductors 
drawn from a copper-clad aluminum rod with the copper 
metallurgically bonded to an aluminum core. The copper 
forms a minimum of 10 percent of the cross-sectional area 
of a solid conductor or each strand of a stranded conductor. 

Cutout Box. An enclosure designed for surface mount- 
ing that has swinging doors or covers secured directly to 
and telescoping with the walls of the box proper. 

Dead Front. Without live parts exposed to a person on 
the operating side of the equipment. 

Demand Factor. The ratio of the maximum demand of 
a system, or part of a system, to the total connected load of 
a system or the part of the system under consideration. 

Device. A unit of an electrical system that is intended 
to carry but not utilize electric energy. 

Disconnecting Means. A device, or group of devices, 
or other means by which the conductors of a circuit can be 
disconnected from their source of supply. 

Dustproof. Constructed or protected so that dust will 
not interfere with its successful operation. 

Dusttight. Constructed so that dust will not enter the 
enclosing case under specified test conditions. 

Duty. 

Continuous Duty. Operation at a substantially constant 
load for an indefinitely long time. 

Intermittent Duty. Operation for alternate intervals of (1) 
load and no load; or (2) load and rest; or (3) load, no load, 
and rest. 

Periodic Duty. Intermittent operation in which the load 
conditions are regularly recurrent. 

Short-Time Duty. Operation at a substantially constant 
load for a short and definitely specified time. 

Varying Duty. Operation at loads, and for intervals of 
time, both of which may be subject to wide variation. 



1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 100 — DEFINITIONS 



70-21 



Dwelling. 

Dwelling Unit. One or more rooms for the use of one or 
more persons as a housekeeping unit with space for eating, 
living, and sleeping, and permanent provisions for cooking 
and sanitation. 

Multifamily Dwelling. A building that contains three or 
more dwelling units. 

One-Family Dwelling. A building that consists solely of 
one dwelling unit. 

Two-Family Dwelling. A building that consists solely of 
two dwelling units. 

Electric Sign. A fixed, stationary, or portable self-con- 
tained, electrically illuminated utilization equipment with 
words or symbols designed to convey information or attract 
attention. 

Enclosed. Surrounded by a case, housing, fence, or walls 
that prevent persons from accidentally contacting energized 
parts. 

Enclosure. The case or housing of apparatus, or the fence 
or walls surrounding an installation to prevent personnel 
from accidentally contacting energized parts, or to protect 
the equipment from physical damage. 

FPN: See Table 430-91 for examples of enclosure types. 

Energized. Electrically connected to a source of poten- 
tial difference. 

Equipment. A general term including material, fittings, 
devices, appliances, fixtures, apparatus, and the like used as 
a part of, or in connection with, an electrical installation. 

Explosionproof Apparatus. Apparatus enclosed in a 
case that is capable of withstanding an explosion of a spec- 
ified gas or vapor that may occur within it and of preventing 
the ignition of a specified gas or vapor surrounding the 
enclosure by sparks, flashes, or explosion of the gas or vapor 
within, and that operates at such an external temperature 
that a surrounding flammable atmosphere will not be ignited 
thereby. 

FPN: For further information, see Explosion-Proof and 
Dust-Ignition-Proof Electrical Equipment for Use in Haz- 
ardous (Classified) Locations, ANSI/UL 1203-1994. 

Exposed (as applied to live parts). Capable of being 
inadvertently touched or approached nearer than a safe dis- 
tance by a person. It is applied to parts that are not suitably 
guarded, isolated, or insulated. 

Exposed (as applied to wiring methods). On or 

attached to the surface or behind panels designed to allow 
access. 



Externally Operable. Capable of being operated with- 
out exposing the operator to contact with live parts. 

Feeder. All circuit conductors between the service equip- 
ment, the source of a separately derived system, or other 
power supply source and the final branch-circuit overcurrent 
device. 

Festoon Lighting. A string of outdoor lights that is sus- 
pended between two points. 

Fitting. An accessory such as a locknut, bushing, or 
other part of a wiring system that is intended primarily to 
perform a mechanical rather than an electrical function. 

Garage. A building or portion of a building in which one 
or more self-propelled vehicles carrying volatile flammable 
liquid for fuel or power are kept for use, sale, storage, rental, 
repair, exhibition, or demonstrating purposes, and all that 
portion of a building that is on or below the floor or floors 
in which such vehicles are kept and that is not separated 
therefrom by suitable cutoffs. 

FPN: For commercial garages, repair, and storage, see Sec- 
tion 511-1. 

Ground. A conducting connection, whether intentional 
or accidental, between an electrical circuit or equipment and 
the earth, or to some conducting body that serves in place 
of the earth. 

Grounded. Connected to earth or to some conducting 
body that serves in place of the earth. 

Grounded, Effectively. Intentionally connected to earth 
through a ground connection or connections of sufficiently 
low impedance and having sufficient current-carrying capac- 
ity to prevent the buildup of voltages that may result in 
undue hazards to connected equipment or to persons. 

Grounded Conductor. A system or circuit conductor 
that is intentionally grounded. 

Grounding Conductor. A conductor used to connect 
equipment or the grounded circuit of a wiring system to a 
grounding electrode or electrodes. 

Grounding Conductor, Equipment. The conductor 
used to connect the noncurrent-carrying metal parts of equip- 
ment, raceways, and other enclosures to the system grounded 
conductor, the grounding electrode conductor, or both, at 
the service equipment or at the source of a separately derived 
system. 

Grounding Electrode Conductor. The conductor used 
to connect the grounding electrode to the equipment ground- 
ing conductor, to the grounded conductor, or to both, of the 
circuit at the service equipment or at the source of a sepa- 
rately derived system. 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-22 



ARTICLE 100 — DEFINITIONS 



Ground-Fault Circuit Interrupter. A device intended 
for the protection of personnel that functions to de-energize 
a circuit or portion thereof within an established period of 
time when a current to ground exceeds some predetermined 
value that is less than that required to operate the overcurrent 
protective device of the supply circuit. 

Ground-Fault Protection of Equipment. A system in- 
tended to provide protection of equipment from damaging 
line-to-ground fault currents by operating to cause a discon- 
necting means to open all ungrounded conductors of the 
faulted circuit. This protection is provided at current levels 
less than those required to protect conductors from damage 
through the operation of a supply circuit overcurrent device. 

Guarded. Covered, shielded, v fenced, enclosed, or other- 
wise protected by means of suitable covers, casings, barriers, 
rails, screens, mats, or platforms to remove the likelihood 
of approach or contact by persons or objects to a point of 
danger. 

Hoistway. Any shaftway, hatchway, well hole, or other 
vertical opening or space in which an elevator or dumbwaiter 
is designed to operate. 

Identified (as applied to equipment). Recognizable as 
suitable for the specific purpose, function, use, environment, 
application, etc., where described in a particular Code re- 
quirement. 

FPN: Suitability of equipment for a specific purpose, envi- 
ronment, or application may be determined by a qualified 
testing laboratory, inspection agency, or other organization 
concerned with product evaluation. Such identification may 
include labeling or listing. (See definitions of Labeled and 
Listed.) 

In Sight From (Within Sight From, Within 
Sight). Where this Code specifies that one equipment shall 
be "in sight from," "within sight from," or "within sight," 
etc., of another equipment, the specified equipment is to be 
visible and not more than 50 ft (15.24 m) distant from the 
other. 

Interrupting Rating. The highest current at rated volt- 
age that a device is intended to interrupt under standard test 
conditions. 

FPN: Equipment intended to interrupt current at other than 
fault levels may have its interrupting rating implied in other 
ratings, such as horsepower or locked rotor current. 

Isolated (as applied to location). Not readily accessible 
to persons unless special means for access are used. 

Labeled. Equipment or materials to which has been 
attached a label, symbol, or other identifying mark of an 
organization that is acceptable to the authority having juris- 
diction and concerned with product evaluation, that main- 



tains periodic inspection of production of labeled equipment 
or materials, and by whose labeling the manufacturer indi- 
cates compliance with appropriate standards or performance 
in a specified manner. 

Lighting Outlet. An outlet intended for the direct con- 
nection of a lampholder, a lighting fixture, or a pendant cord 
terminating in a lampholder. 

Listed. Equipment, materials, or services included in a 
list published by an organization that is acceptable to the 
authority having jurisdiction and concerned with evaluation 
of products or services, that maintains periodic inspection 
of production of listed equipment or materials or periodic 
evaluation of services, and whose listing states that either 
the equipment, material, or services meets identified stand- 
ards or has been tested and found suitable for a specified 
purpose. 

FPN: The means for identifying listed equipment may vary 
for each organization concerned with product evaluation, 
some of which do not recognize equipment as listed unless 
it is also labeled. Use of the system employed by the listing 
organization allows the authority having jurisdiction to iden- 
tify a listed product. 

Live Parts. Electric conductors, buses, terminals, or 
components that are uninsulated or exposed and a shock 
hazard exists. 

Location. 

Damp Location. Partially protected locations under can- 
opies, marquees, roofed open porches, and like locations, 
and interior locations subject to moderate degrees of mois- 
ture, such as some basements, some barns, and some cold- 
storage warehouses. 

Dry Location. A location not normally subject to damp- 
ness or wetness. A location classified as dry may be tempo- 
rarily subject to dampness or wetness, as in the case of a 
building under construction. 

Wet Location. Installations underground or in concrete 
slabs or masonry in direct contact with the earth, and loca- 
tions subject to saturation with water or other liquids, such 
as vehicle washing areas, and locations exposed to weather 
and unprotected. 

Motor Control Center. An assembly of one or more 
enclosed sections having a common power bus and princi- 
pally containing motor control units. 

Multioutlet Assembly. A type of surface, flush, or free- 
standing raceway; designed to hold conductors and recep- 
tacles, assembled in the field or at the factory. 

Nonautomatic. Action requiring personal intervention 
for its control. As applied to an electric controller, nonauto- 



1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 100 — DEFINITIONS 



70-23 



matic control does not necessarily imply a manual controller, 
but only that personal intervention is necessary. 

Nonincendive Circuit. A circuit, other than field wiring, 
in which any arc or thermal effect produced under intended 
operating conditions of the equipment, is not capable, under 
specified test conditions, of igniting the flammable gas-, 
vapor-, or dust-air mixture. 

FPN: For test conditions, see Nonincendive Electrical 
Equipment for Use in Class I and II, Division 2 and Class 
III, Divisions 1 and 2 Hazardous (Classified) Locations, 
ANSI/ISA-SI .2.12-1994. 

Nonincendive Field Wiring. Wiring that enters or 
leaves an equipment enclosure and, under normal operating 
conditions of the equipment, is not capable, due to arcing 
or thermal effects, of igniting the flammable gas- vapor- 
or dust-air mixture. Normal operation includes opening, 
shorting, or grounding the field wiring. 

Nonlinear Load. A load where the wave shape of the 
steady-state current does not follow the wave shape of the 
applied voltage. 

FPN: Electronic equipment, electronic/electric-discharge 
lighting, adjustable-speed drive systems, and similar equip- 
ment may be nonlinear loads. 

Outlet. A point on the wiring system at which current 
is taken to supply utilization equipment. 

Outline Lighting. An arrangement of incandescent 
lamps or electric-discharge lighting to outline or call atten- 
tion to certain features such as the shape of a building or 
the decoration of a window. 

Oven, Wall-Mounted. An oven for cooking purposes 
and consisting of one or more heating elements, internal 
wiring, and built-in or separately mountable controls. 

Overcurrent. Any current in excess of the rated current 
of equipment or the ampacity of a conductor. It may result 
from overload, short circuit, or ground fault. 

FPN: A current in excess of rating may be accommodated 
by certain equipment and conductors for a given set of 
conditions. Therefore the rules for overcurrent protection 
are specific for particular situations. 

Overload. Operation of equipment in excess of normal, 
full-load rating, or of a conductor in excess of rated ampacity 
that, when it persists for a sufficient length of time, would 
cause damage or dangerous overheating. A fault, such as a 
short circuit or ground fault, is not an overload. 

Panelboard. A single panel or group of panel units de- 
signed for assembly in the form of a single panel; including 
buses, automatic overcurrent devices, and equipped with or 



without switches for the control of light, heat, or power 
circuits; designed to be placed in a cabinet or cutout box 
placed in or against a wall or partition and accessible only 
from the front. > 

Plenum. A compartment or chamber to which one or 
more air ducts are connected and that forms part of the air 
distribution system. 

Power Outlet. An enclosed assembly that may include 
receptacles, circuit breakers, fuseholders, fused switches, 
buses, and watt-hour meter mounting means; intended to 
supply and control power to mobile homes, recreational 
vehicles, park trailers, or boats; or to serve as a. means for 
distributing power required to operate mobile or temporarily 
installed equipment. 

Premises Wiring (System). That interior and exterior 
wiring, including power, lighting, control, and signal circuit 
wiring together with all of their associated hardware, fittings, 
and wiring devices, both permanently and temporarily 
installed, that extends from the service point of utility con- 
ductors or source of power such as a battery, a solar photo- 
voltaic system, or a generator, transformer, or converter 
windings, to the outlet(s). Such wiring does not include 
wiring internal to appliances, fixtures, motors, controllers, 
motor control centers, and similar equipment. 

Qualified Person. One familiar with the construction 
and operation of the equipment and the hazards involved. 

Raceway. An enclosed channel of metal or nonmetallic 
materials designed expressly for holding wires, cables, or 
busbars, with additional functions as permitted in this Code. 
Raceways include, but are not limited to, rigid metal conduit, 
rigid nonmetallic conduit, intermediate metal conduit, liq- 
uidtight flexible conduit, flexible metallic tubing, flexible 
metal conduit, electrical nonmetallic tubing, electrical metal- 
lic tubing, underfloor raceways, cellular concrete floor race- 
ways, cellular metal floor raceways, surface raceways, 
wireways, and busways. 

Rainproof. Constructed, protected, or treated so as to 
prevent rain from interfering with the successful operation 
of the apparatus under specified test conditions. 

Raintight. Constructed or protected so that exposure to 
a beating rain will not result in the entrance of water under 
specified test conditions. 

Receptacle. A receptacle is a contact device installed at 
the outlet for the connection of an attachment plug. A single 
receptacle is a single contact device with no other contact 
device on the same yoke. A multiple receptacle is two or 
more contact devices on the same yoke. 

Receptacle Outlet. An outlet where one or more recep- 
tacles are installed. 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-24 



ARTICLE 100 — DEFINITIONS 



Remote-Control Circuit. Any electric circuit that con- 
trols any other circuit through a relay or an equivalent device. 

Sealable Equipment. Equipment enclosed in a case or 
cabinet that is provided with a means of sealing or locking 
so that live parts cannot be made accessible without opening 
the enclosure. The equipment may or may not be operable 
without opening the enclosure. 

Separately Derived System. A premises wiring system 
whose power is derived from a battery, a solar photovoltaic 
system, or from a generator, transformer, or converter wind- 
ings, and that has no direct electrical connection, including 
a solidly connected grounded circuit conductor, to supply 
conductors originating in another system. 

Service. The conductors and equipment for delivering 
electric energy from the serving utility to the wiring system 
of the premises served. 

Service Cable. Service conductors made up in the form 
of a cable. 

Service Conductors. The conductors from the service 
point to the service disconnecting means. 

Service Drop. The overhead service conductors from 
the last pole or other aerial support to and including the 
splices, if any, connecting to the service-entrance conductors 
at the building or other structure. 

Service-Entrance Conductors, Overhead System. The 

service conductors between the terminals of the service 
equipment and a point usually outside the building, clear of 
building walls, where joined by tap or splice to the service 
drop. 

Service-Entrance Conductors, Underground System. 

The service conductors between the terminals of the service 
equipment and the point of connection to the service lateral. 

FPN: Where service equipment is located outside the build- 
ing walls, there may be no service-entrance conductors, or 
they may be entirely outside the building. 

Service Equipment. The necessary equipment, usually 
consisting of a circuit breaker(s) or switch(es) and fuse(s) 
and their accessories, connected to the load end of service 
conductors to a building or other structure, Or an otherwise 
designated area, and intended to constitute the main control 
and cutoff of the supply. 

Service Lateral. The underground service conductors 
between the street main, including any risers at a pole or 
other structure or from transformers, and the first point of 
connection to the service-entrance conductors in a terminal 
box or meter or other enclosure, inside or outside the building 
wall. Where there is no terminal box, meter, or other enclo- 



sure, the point of connection shall be considered to be the 
point of entrance of the service conductors into the building. 

Service Point. The point of connection between the 
facilities of the serving utility and the premises wiring. 

Show Window. Any window used or designed to be 
used for the display of goods or advertising material, whether 
it is fully or partly enclosed or entirely open at the rear and 
whether or not it has a platform raised higher than the street 
floor level. 

Signaling Circuit. Any electric circuit that energizes sig- 
naling equipment. 

Solar Photovoltaic System. The total components and 
subsystems that, in combination, convert solar energy into 
electrical energy suitable for connection to a utilization load. 

Special Permission. The written consent of the authority 
having jurisdiction. 

Switchboard. A large single panel, frame, or assembly 
of panels on which are mounted, on the face or back, or 
both, switches, overcurrent and other protective devices, 
buses, and usually instruments. Switchboards are generally 
accessible from the rear as well as from the front and are 
not intended to be installed in cabinets. 

Switches. 

Bypass Isolation Switch. A manually operated device 
used in conjunction with a transfer switch to provide a means 
of directly connecting load conductors to a power source, 
and of disconnecting the transfer switch. 

General-Use Snap Switch. A form of general-use switch 
constructed so that it can be installed in device boxes or on 
box covers, or otherwise used in conjunction with wiring 
systems recognized by this Code. 

General- Use Switch. A switch intended for use in general 
distribution and branch circuits. It is rated in amperes, and 
it is capable of interrupting its rated current at its rated 
voltage. 

Isolating Switch. A switch intended for isolating an elec- 
tric circuit from the source of power. It has no interrupting 
rating, and it is intended to be operated only after the circuit 
has been opened by some other means. 

Motor-Circuit Switch. A switch rated in horsepower that 
is capable of interrupting the maximum operating overload 
current of a motor of the same horsepower rating as the 
switch at the rated voltage. 

Transfer Switch. An automatic or nonautomatic device 
for transferring one or more load conductor connections 
from one power source to another. 



1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 100 — DEFINITIONS 



70-25 



Thermally Protected (as applied to motors). The 

words "Thermally Protected" appearing on the nameplate 
of a motor or motor-compressor indicate that the motor is 
provided with a thermal protector. 

Thermal Protector (as applied to motors). A protective 
device for assembly as an integral part of a motor or motor- 
compressor that, when properly applied, protects the motor 
against dangerous overheating due to overload and failure 
to start. 

FPN: The thermal protector may consist of one or more 
sensing elements integral with the motor or motor-compres- 
sor and an external control device. 

Utilization Equipment. Equipment that utilizes electric 

energy for electronic, electromechanical, chemical, heating, 

lighting, or similar purposes. 
• 

Ventilated. Provided with a means to permit circulation 

of air sufficient to remove an excess of heat, fumes, or 

vapors. 

Volatile Flammable Liquid. A flammable liquid having 
a flash point below 38°C (100°F), or a flammable liquid 
whose temperature is above its flash point, or a Class II 
combustible liquid having a vapor pressure not exceeding 
40 psia (276 kPa) at 38°C (100°F) whose temperature is 
above its flash point. 

Voltage (of a circuit). The greatest root-mean-square 
(rms) (effective) difference of potential between any two 
conductors of the circuit concerned. 

FPN: Some systems, such as 3-phase 4-wire, single-phase 
3-wire, and 3-wire direct current, may have various circuits 
I of various voltages. 

Voltage, Nominal. A nominal value assigned to a circuit 
or system for the purpose of conveniently designating its 
voltage class (e.g., 120/240 volts, 480Y/277 volts, 600 volts). 

The actual voltage at which a circuit operates can vary 
from the nominal within a range that permits satisfactory 
operation of equipment. 

FPN: See Voltage Ratings for Electric Power Systems and 
I Equipment (60 Hz), ANSI C84.1-1995. 

Voltage to Ground. For grounded circuits, the voltage 
between the given conductor and that point or conductor of 
the circuit that is grounded; for ungrounded circuits, the 
greatest voltage between the given conductor and any other 
conductor of the circuit. 

Watertight. Constructed so that moisture will not enter 
the enclosure under specified test conditions. 

Weatherproof. Constructed or protected so that expo- 
sure to the weather will not interfere with successful oper- 
ation. 



FPN: Rainproof, raintight, or watertight equipment can ful- 
fill the requirements for weatherproof where varying weather 
conditions other than wetness, such as snow, ice, dust, or 
temperature extremes, are not a factor. 

B. Over 600 Volts, Nominal 

Whereas the preceding definitions are intended to apply 
wherever the terms are used throughout this Code, the fol- 
lowing definitions are applicable only to parts of the article 
specifically covering installations and equipment operating 
at over 600 volts, nominal. 

Electronically Actuated Fuse. An overcurrent protec- 
tive device that generally consists of a control module that 
provides current sensing, electronically derived time-current 
characteristics, energy to initiate tripping, and an interrupting 
module that interrupts current when an overcurrent occurs. 
Electronically actuated fuses may or may not operate in a 
current-limiting fashion, depending on the type of control 
selected. 

Fuse. An overcurrent protective device with a circuit- 
opening fusible part that is heated and severed by the passage 
of overcurrent through it. 

FPN: A fuse comprises all the parts that form a unit capable 
of performing the prescribed functions. It may or may not be 
the complete device necessary to connect it into an electrical 
circuit. 

Controlled Vented Power Fuse. A fuse with provision 
for controlling discharge circuit interruption such that no 
solid material may be exhausted into the surrounding at- 
mosphere. 

FPN: The fuse is designed so that discharged gases will not • 
ignite or damage insulation in the path of the discharge or 
propagate a flashover to or between grounded members or 
conduction members in the path of the discharge where the 
distance between the vent and such insulation or conduction 
members conforms to manufacturer's recommendations. 

Expulsion Fuse Unit (Expulsion Fuse). A vented fuse 
unit in which the expulsion effect of gases produced by the 
arc and lining of the fuseholder, either alone or aided by a 
spring, extinguishes the arc. 

Nonvented Power Fuse. A fuse without intentional provi- 
sion for the escape of arc gases, liquids, or solid particles 
to the atmosphere during circuit interruption. 

Power Fuse Unit. A vented, nonvented, or controlled 
vented fuse unit in which the arc is extinguished by being 
drawn through solid material, granular material, or liquid, 
either alone or aided by a spring. 

Vented Power Fuse. A fuse with provision for the escape 
of arc gases, liquids, or solid particles to the surrounding 
atmosphere during circuit interruption. 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-26 



ARTICLE 110 — REQUIREMENTS FOR ELECTRICAL INSTALLATIONS 



Multiple Fuse. An assembly of two or more single-pole 
fuses. 

Switching Device. A device designed to close, open, or 
both, one or more electric circuits. 

Switching Devices. 

Circuit Breaker. A switching device capable of making, 
carrying, and breaking currents under normal circuit condi- 
tions, and also making, carrying for a specified time, and 
breaking currents under specified abnormal circuit condi- 
tions, such as those of short circuit. 

Cutout. An assembly of a fuse support with either a 
fuseholder, fuse carrier, or disconnecting blade. The fuse- 
holder or fuse carrier may include a conducting element 
(fuse link), or may act as the disconnecting blade by the 
inclusion of a nonfusible member. 

Disconnecting (or Isolating) Switch (Disconnector, Iso- 
lator). A mechanical switching device used for isolating a 
circuit or equipment from a source of power. 

Disconnecting Means. A device, group of devices, or 
other means whereby the conductors of a circuit can be 
disconnected from their source of supply. 

Interrupter Switch. A switch capable of making, carry- 
ing, and interrupting specified currents. 

Oil Cutout (Oil-Filled Cutout). A cutout in which all or 
part of the fuse support and its fuse link or disconnecting 
blade is mounted in oil with complete immersion of the 
contacts and the fusible portion of the conducting element 
(fuse link) so that arc interruption by severing of the fuse 
link or by opening of the contacts will occur under oil. 

Oil Switch. A switch having contacts that operate under 
oil (or askarel or other suitable liquid). 

Regulator Bypass Switch. A specific device or combina- 
tion Of devices designed to bypass a regulator. 



Article 110 — Requirements for Electrical 
Installations 

A. General 

110-2. Approval. The conductors and equipment required 
or permitted by this Code shall be acceptable only if ap- 
proved. 

FPN: See Examination of Equipment for Safety, Section 
90-7, and Examination, Identification, Installation, and Use 
of Equipment, Section 110-3. See definitions of Approved, 
Identified, Labeled, and Listed. 



110-3. Examination, Identification, Installation, and Use 
of Equipment. 

(a) Examination. In judging equipment, considerations 
such as the following shall be evaluated: 

(1) Suitability for installation and use in conformity with 
the provisions of this Code 

FPN: Suitability of equipment use may be identified by a 
description marked on or provided with a product to identify 
the suitability of the product for a specific purpose, environ- 
ment, or application. Suitability of equipment may be evi- 
denced by listing or labeling. 

(2) Mechanical strength and durability, including, for parts 
designed to enclose and protect other equipment, the 
adequacy of the protection thus provided 

(3) Wire-bending and connection space 

(4) Electrical insulation 

(5) Heating effects under normal conditions of use and also 
under abnormal conditions likely to arise in service 

(6) Arcing effects 

(7) Classification by type, size, voltage, current capacity, 
and specific use 

(8) Other factors that contribute to the practical safeguard- 
ing of persons using or likely to come in contact with 
the equipment 

(b) Installation and Use. Listed or labeled equipment shall 
be installed and used in accordance with any instructions 
included in the listing or labeling. 

110-4. Voltages. Throughout this Code, the voltage con- 
sidered shall be that at which the circuit operates. The voltage 
rating of electrical equipment shall not be less than the 
nominal voltage of a circuit to which it is connected. 

110-5. Conductors. Conductors normally used to carry 
current shall be of copper unless otherwise provided in this 
Code. Where the conductor material is not specified, the 
material and the sizes given in this Code shall apply to 
copper conductors. Where other materials are used, the size 
shall be changed accordingly. 

FPN: For aluminum and copper-clad aluminum conductors, 
see Section 310-15. 

110-6. Conductor Sizes. Conductor sizes are expressed in 
American Wire Gage (AWG) or in circular mils. 

110-7. Insulation Integrity. Completed wiring installa- 
tions shall be free from short circuits and from grounds other 
than as required or permitted in Article 250. 

110-8. Wiring Methods. Only wiring methods recognized 
as suitable are included in this Code. The recognized meth- 



• 



1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 110 — REQUIREMENTS FOR ELECTRICAL INSTALLATIONS 



70-27 



ods of wiring shall be permitted to be installed in any type 
of building or occupancy, except as otherwise provided in 
this Code. 

110-9. Interrupting Rating. Equipment intended to inter- 
rupt current at fault levels shall have an interrupting rating 
sufficient for the nominal circuit voltage and the current that 
is available at the line terminals of the equipment. 

Equipment intended to interrupt current at other than fault 
levels shall have an interrupting rating at nominal circuit 
voltage sufficient for the current that must be interrupted. 

110-10. Circuit Impedance and Other Characteristics. 

The overcurrent protective devices, the total impedance, the 
component short-circuit current ratings, and other char- 
acteristics of the circuit to be protected shall be selected and 
coordinated to permit the circuit-protective devices used to 
clear a fault to do so without extensive damage to the elec- 
trical components of the circuit. This fault shall be assumed 
to be either between two or more of the circuit conductors, 
or between any circuit conductor and the grounding conduc- 
tor or enclosing metal raceway. Listed products applied in 
accordance with their listing shall be considered to meet the 
requirements of this section. 

110-11. Deteriorating Agents. Unless identified for use in 
the operating environment, no conductors or equipment shall 
be located in damp or wet locations; where exposed to gases, 
fumes, vapors, liquids, or other agents that have a deteriorat- 
ing effect on the conductors or equipment; or where exposed 
to excessive temperatures. 

FPN No. 1: See Section 300-6 for protection against corro- 
sion. 

FPN No. 2: Some cleaning and lubricating compounds can 
cause severe deterioration of many plastic materials used 
for insulating and structural applications in equipment. 

Equipment identified only as "dry locations," "Type 1," 
or "indoor use only" shall be protected against permanent 
damage from the weather during building construction. 

110-12. Mechanical Execution of Work. Electrical equip- 
ment shall be installed in a neat and workmanlike manner. 

(a) Unused Openings. Unused openings in boxes, race- 
ways, auxiliary gutters, cabinets, equipment cases, or hous- 
ings shall be effectively closed to afford protection 
substantially equivalent to the wall of the equipment: 

(b) Subsurface Enclosures. Conductors shall be racked to 
provide ready and safe access in underground and subsurface 
enclosures, into which persons enter for installation and 
maintenance. 

(c) Integrity of Electrical Equipment and Connections. 



Internal parts of electrical equipment, including busbars, 
wiring terminals, insulators, and other surfaces, shall not be 
damaged or contaminated by foreign materials such as paint, 
plaster, cleaners, abrasives, or corrosive residues. There shall 
be no damaged parts that may adversely affect safe operation 
or mechanical strength of the equipment such as parts that 
are broken; bent; cut; or deteriorated by corrosion, chemical 
action, or overheating. 

110-13. Mounting and Cooling of Equipment. 

(a) Mounting. Electrical equipment shall be firmly secured 
to the surface on which it is mounted. Wooden plugs driven 
into holes in masonry, concrete, plaster, or similar materials 
shall not be used. 

(b) Cooling. Electrical equipment that depends upon the 
natural circulation of air and convection principles for cool- 
ing of exposed surfaces shall be installed so that room airflow 
over such surfaces is not prevented by walls or by adjacent 
installed equipment. For equipment designed for floor 
mounting, clearance between top surfaces and adjacent sur- 
faces shall be provided to dissipate rising warm air. 

Electrical equipment provided with ventilating openings 
shall be installed so that walls or other obstructions do not 
prevent the free circulation of air through the equipment. 

110-14. Electrical Connections. Because of different char- 
acteristics of dissimilar metals, devices such as pressure 
terminal or pressure splicing connectors and soldering lugs 
shall be identified for the material of the conductor and shall 
be properly installed and used. Conductors of dissimilar 
metals shall not be intermixed in a terminal or splicing 
connector where physical contact occurs between dissimilar 
conductors (such as copper and aluminum, copper and cop- 
per-clad aluminum, or aluminum and copper-clad alumi- 
num), unless the device is identified for the purpose and 
conditions of use. Materials such as solder, fluxes, inhibitors, 
and compounds, where employed, shall be suitable for the 
use and shall be of a type that will not adversely affect the 
conductors, installation, or equipment. 

FPN: Many terminations and equipment are marked with a 
tightening torque. 

(a) Terminals. Connection of conductors to terminal parts 
shall ensure a thoroughly good connection without damaging 
the conductors and shall be made by means of pressure 
connectors (including set-screw type), solder lugs, or splices 
to flexible leads. Connection by means of wire-binding 
screws or studs and nuts that have upturned lugs or the 
equivalent shall be permitted for No. 10 or smaller conduc- 
tors. 

Terminals for more than one conductor and terminals 
used to connect aluminum shall be so identified. 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-28 



ARTICLE 110 — REQUIREMENTS FOR ELECTRICAL INSTALLATIONS 



(b) Splices. Conductors shall be spliced or joined with 
splicing devices identified for the use or by brazing, welding, 
or soldering with a fusible metal or alloy. Soldered splices 
shall first be spliced or joined so as to be mechanically and 
electrically secure without solder and then soldered. All 
splices and joints and the free ends of conductors shall be 
covered with an insulation equivalent to that of the conduc- 
tors or with an insulating device identified for the purpose. 

Wire connectors or splicing means installed on conduc- 
tors for direct burial shall be listed for such use. 

(c) Temperature Limitations. The temperature rating as- 
sociated with the ampacity of a conductor shall be selected 
and coordinated so as not to exceed the lowest temperature 
rating of any connected termination, conductor, or device. 
Conductors with temperature ratings higher than specified 
for terminations shall be permitted to be used for ampacity 
adjustment, correction, or both. 

(1) Termination provisions of equipment for circuits 
rated 100 amperes or less, or marked for Nos. 14 through 
1 conductors, shall be used only for one of the following. 

(a) Conductors rated 60°C (140°F), or 

(b) Conductors with higher temperature ratings, provided 
the ampacity of such conductors is determined based 
on the 60°C (140°F) ampacity of the conductor size 
used, or 

(c) Conductors with higher temperature ratings if the equip- 
ment is listed and identified for use with such conductors, 
or 

(d) For motors marked with design letters B v , C, D, or E, 
conductors having an insulation rating of 75°C (167°F) 
or higher shall be permitted to be used provided the 
ampacity of such conductors does not exceed the 75°C 
(167°F) ampacity. 

(2) Termination provisions of equipment for circuits 
rated over 100 amperes, or marked for conductors larger 
than No. 1, shall be used only for 

(a) Conductors rated 75°C (167°F), or 

(b) Conductors with higher temperature ratings provided 
the ampacity of such conductors does not exceed the 
75°C (167°F) ampacity of the conductor size used, or 
up to their ampacity if the equipment is listed and identi- 
fied for use with such conductors. 

(3) Separately installed pressure connectors shall be used 
with conductors at the ampacities not exceeding the ampacity 
at the listed and identified temperature rating of the con- 
nector. 

FPN: With respect to Sections 110-14(c)(l), (2), and (3), 
equipment markings or listing information may additionally 



restrict the sizing and temperature ratings of connected con- 
ductors. 

110-18. Arcing Parts. Parts of electric equipment, which 
in ordinary operation produce arcs, sparks, flames, or molten 
metal, shall be enclosed or separated and isolated from all 
combustible material. 

FPN: For hazardous (classified) locations, see Articles 500 
through 517. For motors, see Section 430-14. 

110-19. Light and Power from Railway Conductors. Cir- 
cuits for lighting and power shall not be connected to any 
system that contains trolley wires with a ground return. 

Exception: Car houses, power houses, or passenger and 
freight stations operated in connection with electric rail- 
ways. 

110-21. Marking. The manufacturer's name, trademark, 
or other descriptive marking by which the organization 
responsible for the product can be identified shall be placed 
on all electric equipment. Other markings that indicate volt- 
age, current, wattage, or other ratings shall be provided as 
specified elsewhere in this Code. The marking shall be of 
sufficient durability to withstand the environment involved. 

110-22. Identification of Disconnecting Means. Each dis- 
connecting means required by this Code for motors and 
appliances, and each service, feeder, or branch circuit at the 
point where it originates, shall be legibly marked to indicate 
its purpose unless located and arranged so the purpose is 
evident. The marking shall be of sufficient durability to 
withstand the environment involved. 

Where circuit breakers or fuses are applied in compliance 
with the series combination ratings marked on the equipment 
by the manufacturer, the equipment enclosure(s) shall be 
legibly marked in the field 'to indicate the equipment has 
been applied with a series combination rating. The marking 
shall be readily visible and state the following: 

CAUTION — SERIES COMBINATION SYSTEM 

RATED AMPERES. IDENTIFIED 

REPLACEMENT COMPONENTS REQUIRED. 

FPN: See Section 240-83(c) for interrupting rating marking 
for end-use equipment. 

B. 600 Volts, Nominal, or Less 

110-26. Spaces About Electrical Equipment. Sufficient 
access and working space shall be provided and maintained 
about all electric equipment to permit ready and safe opera- 
tion and maintenance of such equipment. Enclosures housing 
electrical apparatus that are controlled by lock and key shall 
be considered accessible to qualified persons. 

(a) Working Space. Working space for equipment operat- 
ing at 600 volts, nominal, or less to ground and likely to 



1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 1 10 — REQUIREMENTS FOR ELECTRICAL INSTALLATIONS 



70-29 



require examination, adjustment, servicing, or maintenance 
while energized shall comply with the dimensions of (1), 
(2), and (3) or as required or permitted elsewhere in this 
Code. 

(1) Depth of Working Space. The depth of the working 

space in the direction of access to live parts shall not be 

less than indicated in Table 110-26(a). Distances shall be 

measured from the live parts if such are exposed or from 

I the enclosure front or opening if such are enclosed. 

I Table 110-26(a). Working Spaces 





Minimum Clear Distance (ft) 


1 Nominal Voltage 
to Ground 


Condition 
1 


Condition 

2 


Condition 
3 


0-150 
151-600 


3 
3 


3 

3'/2 


3 
4 



Notes: 

1. For SI units, 1 ft = 0.3048 m. 

2. Where the conditions are as follows: 

Condition 1 — Exposed live parts on one side and no live or grounded 
parts on the other side of the working space, or exposed live parts on 
both sides effectively guarded by suitable wood or other insulating materi- 
als. Insulated wire or insulated busbars operating at not over 300 volts 
to ground shall not be considered live parts. 

Condition 2 — Exposed live parts on one side and grounded parts on 
the other side. Concrete, brick, or tile walls shall be considered as 
grounded. 

Condition 3 — Exposed live parts on both sides of the work space (not 
guarded as provided in Condition 1) with the operator between. 



Exception No. 1: Working space shall not be required in 
back or sides of assemblies, such as dead-front switchboards 
or motor control centers, where there are no renewable or 
adjustable parts, such as fuses or switches, on the back or 
sides and where all connections are accessible from loca- 
tions other than the back or sides. Where rear access is 
required to work on de-energized parts on the back of en- 
closed equipment, a minimum working space of 30 in. (762 
mm) horizontally shall be provided. 

Exception No. 2: By special permission, smaller spaces shall 
be permitted where all uninsulated parts are at a voltage no 
greater than 30 volts rms, 42 volts peak, or 60 volts dc. 

Exception No. 3: In existing buildings where electrical 
equipment is being replaced, Condition 2 working clearance 
shall be permitted between dead-front switchboards, panel- 
boards, or motor control centers located across the aisle 
from each other where conditions of maintenance and su- 
pervision ensure that written procedures have been adopted 
to prohibit equipment on both sides of the aisle from being 
open at the same time and qualified persons who are autho- 
rized will service the installation. 



(2) Width of Working Space. The width of the working 
space in front of the electric equipment shall be the width 
of the equipment or 30 in. (762 mm), whichever is greater. 
In all cases, the work space shall permit at least a 90 degree 
opening of equipment doors or hinged panels. 

(3) Height of Working Space. The work space shall be 
clear and extend from the grade, floor, or platform to the 
height required by Section 110-26(e). Within the height re- 
quirements of this section, other equipment associated with 
the electrical installation located above or below the electri- 
cal equipment shall be permitted to extend not more than 6 
in. (153 mm) beyond the front of the electrical equipment. 

(b) Clear Spaces. Working space required by this section 
shall not be used for storage. When normally enclosed live 
parts are exposed for inspection or servicing, the working 
space, if in a passageway or general open space, shall be 
suitably guarded. 

(c) Access and Entrance to Working Space. At least one 
entrance of sufficient area shall be provided to give access 
to the working space about electric equipment. 

For equipment rated 1200 amperes or more and over 6 ft 
(1.83 m) wide that contains overcurrent devices, switching 
devices, or control devices, there shall be one entrance not 
less than 24 in. (610 mm) wide and 6!/2 ft (1.98 m) high at 
each end of the working space. 

Exception No. 1: Where the location permits a continuous 
and unobstructed way of exit travel, one means of access 
shall be permitted. 

Exception No. 2: Where the work space required by Section 
110-26(a) is doubled, only one entrance to the working space 
is required. It shall be located so the edge of the entrance 
nearest the equipment is the minimum clear distance given 
in Table 110-26(a) away from such equipment. 

(d) Illumination. Illumination shall be provided for all 
working spaces about service equipment, switchboards, pan- 
elboards, or motor control centers installed indoors. Addi- 
tional lighting fixtures shall not be required where the work 
space is illuminated by an adjacent light source. In electrical 
equipment rooms, the illumination shall not be controlled 
by automatic means only. 

(e) Headroom. The minimum headroom of working spaces 
about service equipment, switchboards, panelboards, or 
motor control centers shall be 614 ft (1.98 m). Where the 
electrical equipment exceeds 6V2 ft (1.98 m) in height, the 
minimum headroom shall not be less than the height of 
the equipment. 

Exception: Service equipment or panelboards, in existing 
dwelling units, that do not exceed 200 amperes. 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-30 



ARTICLE 110 — REQUIREMENTS FOR ELECTRICAL INSTALLATIONS 



(f) Dedicated Equipment Space. Equipment within the 
scope of Article 384, and motor control centers, shall be 
located in dedicated spaces and protected from damage as 
covered in (1) and (2). 

Exception: Control equipment that by its very nature or 
because of other rules of the Code must be adjacent to or 
within sight of its operating machinery shall be permitted 
in those locations. 

(1) Indoor. For indoor installations, the dedicated space 
shall comply with the following. 

(a) Dedicated Electrical Space. The space equal to the 
width and depth of the equipment and extending from the 
floor to a height of 6 ft (1.83 m) above the equipment or to 
the structural ceiling, whichever is lower, shall be dedicated 
to the electrical installation. No piping, ducts, or equipment 
foreign to the electrical installation shall be located in this 
zone. 

Exception: Equipment that is isolated from the foreign 
equipment by height or physical enclosures or covers that 
will afford adequate mechanical protection from vehicular 
traffic or accidental contact by unauthorized personnel or 
that complies with (b), shall be permitted in areas that do 
not have the dedicated space described in this rule. 

(b) Foreign Systems. The space equal to the width and 
depth of the equipment shall be kept clear of foreign systems 
unless protection is provided to avoid damage from conden- 
sation, leaks, or breaks in such foreign systems. This zone 
shall extend from the top of the electrical equipment to the 
structural ceiling. 

(c) Sprinkler Protection. Sprinkler protection shall be 
permitted for the dedicated space where the piping complies 
with this section. 

(d) Suspended Ceilings. A dropped, suspended, or simi- 
lar ceiling that does not add strength to the building structure 
shall not be considered a structural ceiling. 

(2) Outdoor. Outdoor electrical equipment shall be in- 
stalled in suitable enclosures and shall be protected from 
accidental contact by unauthorized personnel, or by vehicu- 
lar traffic, or by accidental spillage or leakage from piping 
systems. The working clearance space shall include the zone 
described in Section 110-26(a). No architectural appurte- 
nance or other equipment shall be located in this zone. 

110-27. Guarding of Live Parts. 

(a) Live Parts Guarded Against Accidental Contact. Ex- 
cept as elsewhere required or permitted by this Code, live 
parts of electric equipment operating at 50 volts or more 
shall be guarded against accidental contact by approved 
enclosures or by any of the following means. 



(1) By location in a room, vault, or similar enclosure that 
is accessible only to qualified persons. 

(2) By suitable permanent, substantial partitions or screens 
arranged so that only qualified persons will have access 
to the space within reach of the live parts. Any openings 
in such partitions or screens shall be sized and located 
so that persons are not likely to come into accidental 
contact with the live parts or to bring conducting objects 
into contact with them. 

(3) By location on a suitable balcony, gallery, or platform 
elevated and arranged so as to exclude unqualified per- 
sons. 

(4) By elevation of 8 ft (2.44 m) or more above the floor 
or other working surface. 

(b) Prevent Physical Damage. In locations where electric 
equipment is likely to be exposed to physical damage, enclo- 
sures or guards shall be so arranged and of such strength as 
to prevent such damage. 

(c) Warning Signs. Entrances to rooms and other guarded 
locations that contain exposed live parts shall be marked with 
conspicuous warning signs forbidding unqualified persons to 
enter. 

FPN: For motors, see Sections 430-132 and 430-133. For 
over 600 volts, see Section 1 10-34. 



C. Over 600 Volts, Nominal 

110-30. General. Conductors and equipment used on cir- 
cuits over 600 volts, nominal, shall comply with Part A of 
this article and with the following sections, which supple- 
ment or modify Part A. In no case shall the provisions of 
this part apply to equipment on the supply side of the service 
point. 

110-31. Enclosure for Electrical Installations. Electrical 
installations in a vault, room, or closet or in an area sur- 
rounded by a wall, screen, or fence, access to which is 
controlled by lock and key or other approved means, shall 
be considered to be accessible to qualified persons only. The 
type of enclosure used in a given case shall be designed 
and constructed according to the nature and degree of the 
hazard(s) associated with the installation. 

For installations other than equipment as described in 
Section 110-3 1(c), a wall, screen, or fence shall be used to 
enclose an outdoor electrical installation to deter access by 
persons who are not qualified. A fence shall not be less than 
7 ft (2.13 m) in height or a combination of 6 ft (1.80 m) or 
more offence fabric and a 1-ft (305-mm) or more extension 
utilizing three or more strands of barbed wire or equivalent. 

FPN: See Article 450 for construction requirements for 
transformer vaults. 



1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 110 — REQUIREMENTS FOR ELECTRICAL INSTALLATIONS 



70-31 



• 



• 



(a) Indoor Installations. 

(1) In Places Accessible to Unqualified Persons. In- 
door electrical installations that are open to unqualified per- 
sons shall be made with metal-enclosed equipment or shall 
be enclosed in a vault or in an area to which access is 
controlled by a lock. Metal-enclosed switchgear, unit sub- 
stations, transformers, pull boxes, connection boxes, and 
other similar associated equipment shall be marked with 
appropriate caution signs. Openings in ventilated dry-type 
transformers or similar openings in other equipment shall 
be designed so that foreign objects inserted through these 
openings will be deflected from energized parts. 

(2) In Places Accessible to Qualified Persons Only. 

Indoor electrical installations considered accessible only to 
qualified persons in accordance with this section shall com- 
ply with Sections 110-34, 110-35, and 110-36. 

(b) Outdoor Installations. 

(1) In Places Accessible to Unqualified Persons. Out- 
door electrical installations that are open to unqualified per- 
sons shall comply with Article 225. 

FPN: For clearances of conductors for system voltages over 
600 volts, nominal, see National Electrical Safety Code, 
ANSI C2-1997. 

(2) In Places Accessible to Qualified Persons Only. 

Outdoor electrical installations that have exposed live parts 
shall be accessible to qualified persons only in accordance 
with the first paragraph of this section and shall comply 
with Sections 110-34, 110-35, and 110-36. 

(c) Enclosed Equipment Accessible to Unqualified Per- 
sons. Ventilating or similar openings in equipment shall 
be designed so that foreign objects inserted through these 
openings will be deflected from energized parts. Where ex- 
posed to physical damage from vehicular traffic, suitable 
guards shall be provided. Nonmetallic or metal-enclosed 
equipment located outdoors and accessible to the general 
public shall be designed so that exposed nuts or bolts cannot 
be readily removed, permitting access to live parts. Where 
nonmetallic or metal-enclosed equipment is accessible to 
the general public and the bottom of the enclosure is less 
than 8 ft (2.44 m) above the floor or grade level, the enclosure 
door or hinged cover shall be kept locked. Doors and covers 
of enclosures used solely as pull boxes, splice boxes, or 
junction boxes shall be locked, bolted, or screwed on. Under- 
ground box covers that weigh over 100 lb (45.4 kg) shall 
be considered as meeting this requirement. 

110-32. Work Space About Equipment. Sufficient space 
shall be provided and maintained about electric equipment 
to permit ready and safe operation and maintenance of such 
equipment. Where energized parts are exposed, the minimum 



clear work space shall not be less than 6 ) /2 ft (1.98 m) high 
(measured vertically from the floor or platform), or less than 
3 ft (914 mm) wide (measured parallel to the equipment). 
The depth shall be as required in Section 110-34(a). In all 
cases, the work space shall be adequate to permit at least a 
90 degree opening of doors or hinged panels. 

110-33. Entrance and Access to Work Space. 

(a) Entrance. At least one entrance not less than 24 in. 
(610 mm) wide and 6!/2 ft (1.98 m) high shall be provided 
to give access to the working space about electric equipment. 

(1) On switchboard and control panels exceeding 6 ft 
(1.83 m) in width, there shall be one entrance at each end 
of such boards unless the location of the switchboards and 
control panels permits a continuous and unobstructed way 
of exit travel, or unless the work space required in Section 
110-34(a) is doubled. 

(2) Where one entrance to the working space is permitted 
under the conditions described in (1), the entrance shall be 
located so that the edge of the entrance nearest the switch- 
boards and control panels is the minimum clear distance 
given in Table 110-34(a) away from such equipment. 

(3) Where bare energized parts at any voltage or insulated 
energized parts above 600 volts, nominal, to ground are 
located adjacent to such entrance, they shall be suitably 
guarded. 

(b) Access. Permanent ladders or stairways shall be pro- 
vided to give safe access to the working space around electric 
equipment installed on platforms, balconies, mezzanine 
floors, or in attic or roof rooms or spaces. 

110-34. Work Space and Guarding. 

(a) Working Space. Except as elsewhere required or per- 
mitted in this Code, the minimum clear working space in 
the direction of access to live parts of electrical equipment 
shall not be less than specified in Table 1 10-34(a). Distances 
shall be measured from the live parts, if such are exposed, 
or from the enclosure front or opening if such are enclosed. 

Exception: Working space shall not be required in back 
of equipment such as dead-front switchboards or control 
assemblies where there are no renewable or adjustable parts 
(such as fuses or switches) on the back and where all con- 
nections are accessible from locations other than the back. 
Where rear access is required to work on de-energized parts 
on the back of enclosed equipment, a minimum working 
space of 30 in. (762 mm) horizontally shall be provided. 

(b) Separation from Low-Voltage Equipment. Where 
switches, cutouts, or other equipment operating at 600 volts, 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-32 



ARTICLE 110 — REQUIREMENTS FOR ELECTRICAL INSTALLATIONS 



Table 110-34(a). Minimum Depth of Clear Working Space at 
Electrical Equipment 

Minimum Clear Distance (ft) 



Nominal Voltage 
to Ground 


Condition 
1 


Condition 

2 


Condition 
3 


601-2500 V 
2501-9000 V 
9001-25,000 V 
25,001-75 kV 
Above 75 kV 


3 
4 
5 
6 
8 


4 
5 
6 
8 
10 


5- 

6 

9 

10 

12 



Notes: 

1. For SI units, 1 ft =,0.3048 m. 

12. Where the conditions are as follows: 
Condition 1 — Exposed live parts on one side and no live or grounded 
parts on the other side of the working space, or exposed live parts on 
both sides effectively guarded by suitable wood or other insulating materi- 
als. Insulated wire or insulated busbars operating at not over 300 volts 
shall not be considered live parts. 

I Condition 2 — Exposed live parts on one side and grounded parts on 
the other side. Concrete, brick, or tile walls will be considered as 
grounded surfaces. 

I Condition 3 — Exposed live parts on both sides of the work space (not 
guarded as provided in Condition 1) with the operator between. 



nominal, or less, are installed in a room or enclosure where 
there are exposed live parts or exposed wiring operating at 
over 600 volts, nominal, the high-voltage equipment shall 
be effectively separated from the space occupied by the low- 
voltage equipment by a suitable partition, fence, or screen. 

Exception: Switches or other equipment operating at 600 
volts, nominal, or less, and serving only equipment within 
the high-voltage vault, room, or enclosure shall be permitted 
to be installed in the high-voltage enclosure, room, or vault 
if accessible to qualified persons only. 

(c) Locked Rooms or Enclosures. The entrances to all 
buildings, rooms, or enclosures containing exposed live 
parts or exposed conductors operating at over 600 volts, 
nominal, shall be kept locked unless such entrances are under 
the observation of a qualified person at all times. 

Where the voltage exceeds 600 volts, nominal, permanent 
and conspicuous warning signs shall be provided, reading 
as follows: 

DANGER — HIGH VOLTAGE — KEEP OUT 

(d) Illumination. Illumination shall be provided for all 
working spaces about electrical equipment. The lighting out- 
lets shall be arranged so that persons changing lamps or 
making repairs on the lighting system will not be endangered 
by live parts or other equipment. 

The points of control shall be located so that persons are 
not likely to come in contact with any live part or moving 
part of the equipment while turning on the lights. 



(e) Elevation of Unguarded Live Parts. Unguarded live 
parts above working space shall be maintained at elevations 
not less than required by Table 110-34(e). 

Table 110-34(e). Elevation of Unguarded Live Parts Above 
Working Space 



Nominal Voltage 
Between Phases 



Elevation 



601-7500 V 
7501-35,000 V 
Over 35 kV 



8 ft 6 in. 

9 ft 

9 ft + 0.37 in./kV above 35 



Note: For SI units, 1 in. = 25.4 mm; 1 ft = 0.3048 m. 

(f) Protection of Service Equipment, Metal-Enclosed 
Power Switchgear, and Industrial Control Assemblies. 

Pipes or ducts foreign to the electrical installation that require 
periodic maintenance or whose malfunction would endanger 
the operation of the electrical system shall not be located in 
the vicinity of the service equipment, metal-enclosed power 
switchgear, or industrial control assemblies. Protection shall 
be provided where necessary to avoid damage from conden- 
sation leaks and breaks in such foreign systems. Piping and 
other facilities shall not be considered foreign if provided 
for fire protection of the electrical installation. 

110-36. Circuit Conductors. Circuit conductors shall be 
permitted to be installed in raceways, in cable trays, as metal- 
clad cable, as bare wire, cable, and busbars, or as Type MV 
cables, or conductors as provided in Sections 300-37, 300- 
39, 300-40, and 300-50. Bare live conductors shall conform 
with Section 490-24. 

Insulators, together with their mounting and conductor 
attachments, where used as supports for wires, single-con- 
ductor cables, or busbars, shall be capable of safely with- 
standing the maximum magnetic forces that would prevail 
when two or more conductors of a circuit were subjected to 
short-circuit current. 

Open runs of insulated wires and cables that have a bare 
lead sheath or a braided outer covering shall be supported 
in a manner designed to prevent physical damage to the 
braid or sheath. Supports for lead-covered cables shall be 
designed to prevent electrolysis of the sheath. 

110-40. Temperature Limitations at Terminations. Con- 
ductors shall be permitted to be terminated based on the 
90°C (194°F) temperature rating and ampacity as given in 
Tables 310-67 through 310-86, unless otherwise identified. 

D. Tunnel Installations Over 600 Volts, Nominal 

110-51. General. 

(a) Covered. The provisions of this part shall apply to in- 
stallation and use of high-voltage power distribution and 



1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 1 10 — REQUIREMENTS FOR ELECTRICAL INSTALLATIONS 



70-33 



utilization equipment that is portable and/or mobile, such 
as substations, trailers, or cars, mobile shovels, draglines, 
hoists, drills, dredges, compressors, pumps, conveyors, un- 
derground excavators, and the like. 

(b) Other Articles. The requirements of this part shall be 
additional to, or amendatory of, those prescribed in Articles 
100 through 490 of this Code. Special attention shall be 
paid to Article 250. 

(c) Protection Against Physical Damage. Conductors and 
cables in tunnels shall be located above the tunnel floor and 
so placed or guarded to protect them from physical damage. 

110-52. Overcurrent Protection. Motor-operated equip- 
ment shall be protected from overcurrent in accordance with 
Article 430. Transformers shall be protected from over- 
current in accordance with Article 450. 

110-53. Conductors. High-voltage conductors in tunnels 
shall be installed in metal conduit or other metal raceway, 
Type MC cable, or other approved multiconductor cable. 
Multiconductor portable cable shall be permitted to supply 
mobile equipment. 

110-54. Bonding and Equipment Grounding Conduc- 
tors. 

(a) Grounded and Bonded. All noncurrent-carrying metal 
parts of electric equipment and all metal raceways and cable 
sheaths shall be effectively grounded and bonded to all metal 
pipes and rails at the portal and at intervals not exceeding 
1000 ft (305 m) throughout the tunnel. 



(b) Equipment Grounding Conductors. An equipment 
grounding conductor shall be run with circuit conductors 
inside the metal raceway or inside the multiconductor cable 
jacket. The equipment grounding conductor shall be permit- 
ted to be insulated or bare. 

110-55. Transformers, Switches, and Electrical Equip- 
ment. All transformers, switches, motor controllers, motors, 
rectifiers, and other equipment installed below ground shall 
be protected from physical damage by location or guarding. 

110-56. Energized Parts. Bare terminals of transformers, 
switches, motor controllers, and other equipment shall be 
enclosed to prevent accidental contact with energized parts. 

110-57. Ventilation System Controls. Electrical controls 
for the ventilation system shall be arranged so that the airflow 
can be reversed. 

110-58. Disconnecting Means. A switching device, meet- 
ing the requirements of Article 430 or 450, shall be installed 
at each transformer or motor location for disconnecting the 
transformer or motor. The switching device shall open all 
ungrounded conductors of a circuit simultaneously. 

110-59. Enclosures. Enclosures for use in tunnels shall be 
dripproof, weatherproof, or submersible as required by the 
environmental conditions. Switch or contactor enclosures 
shall not be used as junction boxes or raceways for conduc- 
tors feeding through or tapping off to other switches, unless 
special designs are used to provide adequate space for this 
purpose. 



NATIONAL ELECTRICAL CODE 



1999 Edition 



ARTICLE 200 — USE AND IDENTIFICATION OF GROUNDED CONDUCTORS 



70-35 



CHAPTER 2 
Wiring and Protection 

Article 200 — Use and Identification of Grounded 
Conductors 

200-1. Scope. This article provides requirements for the 
following: 

(1) Identification of terminals 

(2) Grounded conductors in premises wiring systems 

(3) Identification of grounded conductors 

FPN: See Article 100 for definitions of Grounded Conduc- 
tor and Grounding Conductor. 

200-2. General. All premises wiring systems, other than 
circuits and systems exempted or prohibited by Sections 
210-10, 215-7, 250-21, 250-22, 250-162, 503-13, 517-63, 
668-11, 668-21, and Section 690-41, Exception, shall have 
a grounded conductor that is identified in accordance with 
Section 200-6. 

The grounded conductor, where insulated, shall have in- 
sulation that is (1) suitable, other than color, for any un- 
grounded conductor of the same circuit on circuits of less 
than 1000 volts or impedance grounded neutral systems of 
1 kV and over, or (2) rated not less than 600 volts for solidly 
grounded neutral systems of 1 kV and over as described in 
Section 250- 184(a). 

200-3. Connection to Grounded System. Premises wiring 
shall not be electrically connected to a supply system unless 
the latter contains, for any grounded conductor of the interior 
system, a corresponding conductor that is grounded. For the 
purpose of this section, electrically connected shall mean 
connected so as to be capable of carrying current, as distin- 
guished from connection through electromagnetic induction. 

200-6. Means of Identifying Grounded Conductors. 

(a) Sizes No. 6 or Smaller. An insulated grounded con- 
ductor of No. 6 or smaller shall be identified by a continuous 
white or natural gray outer finish or by three continuous 
white stripes on other than green insulation along its entire 
length. Wires that have their outer covering finished to show 
a white or natural gray color but have colored tracer threads 
in the braid identifying the source of manufacture shall be 
considered as meeting the provisions of this section. Insu- 
lated grounded conductors shall also be permitted to be 
identified as follows. 

(1) The grounded conductor of a mineral-insulated, 
metal-sheathed cable shall be identified at the time of instal- 
lation by distinctive marking at its terminations. 



(2) A single-conductor, sunlight-resistant, outdoor-rated 
cable used as a grounded conductor in photovoltaic power 
systems as permitted by Section 690-31 shall be identified 
at the time of installation by distinctive white marking at 
all terminations. 

(3) Fixture wire shall comply with the requirements for 
grounded conductor identification as specified in Section 
402-8. 

(4) For aerial cable, the identification shall be as above, 
or by means of a ridge located on the exterior of the cable 
so as to identify it. 

(b) Sizes Larger than No. 6. An insulated grounded con- 
ductor larger than No. 6 shall be identified either by a con- 
tinuous white or natural gray outer finish or by three continu- 
ous white stripes on other than green insulation along 
its entire length or at the time of installation by a distinctive 
white marking at its terminations. This marking shall encircle 
the conductor or insulation. 



(c) Flexible Cords. An insulated conductor that is intended 
for use as a grounded conductor, where contained within a 
flexible cord, shall be identified by a white or natural gray 
outer finish or by three continuous white stripes on other 
than green insulation or by methods permitted by Section 
400-22. 

(d) Grounded Conductors of Different Systems. Where 
conductors of different systems are installed in the same 
raceway, cable, box, auxiliary gutter, or other type of enclo- 
sure, one system grounded conductor, if required, shall have 
an outer covering conforming to Section 200-6(a) or 
200-6(b). Each other system grounded conductor shall have 
an outer covering of white with a readily distinguishable 
different colored stripe (not green) running along the insula- 
tion, or other and different means of identification as allowed 
by Section 200-6(a) or (b) that will distinguish each system 
grounded conductor. 

(e) Grounded Conductors of Multiconductor Cables. 

The insulated grounded conductors in a multiconductor cable 
shall be identified by a continuous white or natural gray 
outer finish or by three continuous white stripes on other 
than green insulation along its entire length. Multiconductor 
flat cable No. 4 or larger shall be permitted to employ an 
external ridge on the grounded conductor. 

Exception No. 1: Where the conditions of maintenance and 
supervision ensure that only qualified persons will service 
the installation, grounded conductors in multiconductor ca- 
bles shall be permitted to be permanently identified at their 
terminations at the time of installation by a distinctive white 
marking or other equally effective means. 



NATIONAL ELECTRICAL CODE 



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70-36 



ARTICLE 200 — USE AND IDENTIFICATION OF GROUNDED CONDUCTORS 



Exception No. 2: The grounded conductor of a multicon- 
ductor varnished-cloth-insulated cable shall be permitted to 
be identified at its terminations at the time of installation 
by a distinctive white marking or other equally effective 
means. 

200-7. Use of Insulation of a White or Natural Gray 
Color or with Three Continuous White Stripes. 

(a) General. The following shall be used only for the 
grounded circuit conductor, unless otherwise permitted in 

(b) and (c): 

(1) A conductor with continuous white or natural gray cov- 
ering 

(2) A conductor with three continuous white stripes on other 
than green insulation 

(3) A marking at the termination of white or natural gray 
color 

(b) Circuits of Less than 50 Volts. A conductor with white 
or natural gray color insulation or three continuous white 
stripes or having a marking of white or natural gray at the 
termination for circuits of less than 50 volts shall be required 
to be grounded only as required by Section 250-20(a). 

(c) Circuits of 50 Volts or More. The use of insulation 
that is white or natural gray or that has three continuous 
white stripes for other than a grounded conductor for cir- 
cuits of 50 volts or more shall be permitted only as in (1) 
through (3). 

(1) If part of a cable assembly and where the insulation 
is permanently re-identified to indicate its use as an un- 
grounded conductor, by painting or other effective means 
at its termination, and at each location Where the conductor 
is visible and accessible. 

(2) Where a cable contains an insulated conductor for 
single-pole, 3-way, or 4-way switch loops, and the conductor 
with white or natural gray insulation or a marking of three 
continuous white stripes is used for the supply to the switch, 
but not as a return conductor from the switch to the switched 
outlet. In these applications, the conductor with white or 
natural gray insulation or with three continuous white stripes 
shall be permanently re-identified to indicate its use by 
painting or other effective means at its terminations and at 
each location where the conductor is visible and accessible. 

(3) Where a flexible cord, having one conductor identi- 
fied by a white or natural gray outer finish or three continu- 
ous white stripes or by any other means permitted by Section 
400-22, is used for connecting an appliance or equipment 
permitted by Section 400-7. This shall apply to flexible cords 
connected to outlets whether or not the outlet is supplied by 
a circuit that has a grounded conductor. 



200-9. Means of Identification of Terminals. The identi- 
fication of terminals to which a grounded conductor is to 
be connected shall be substantially white in color. The identi- 
fication of other terminals shall be of a readily distin- 
guishable different color. 

Exception: Where the conditions of maintenance and super- 
vision ensure that only qualified persons will service the 
installations, terminals for grounded conductors shall be 
permitted to be permanently identified at the time of instal- 
lation by a distinctive white marking or other equally effec- 
tive means. 

200-10. Identification of Terminals. 

(a) Device Terminals. All devices, excluding lighting and 
appliance branch-circuit panelboards, provided with termi- 
nals for the attachment of conductors and intended for con- 
nection to more than one side of the circuit shall have 
terminals properly marked for identification, unless the elec- 
trical connection of the terminal intended to be connected 
to the grounded conductor is clearly evident. 

Exception: Terminal identification shall not be required for 
devices that have a normal current rating of over 30 amperes, 
other than polarized attachment plugs and polarized recep- 
tacles for attachment plugs as required in Section 200-10(b). 

(b) Receptacles, Plugs, and Connectors. Receptacles, po- 
larized attachment plugs, and cord connectors for plugs and 
polarized plugs shall have the terminal intended for con- 

I nection to the grounded conductor identified. 

Identification shall be by a metal or metal coating that 
is substantially white in color or by the word white or the 
letter W located adjacent to the identified terminal. 

If the terminal is not visible, the conductor entrance hole 
for the connection shall be colored white or marked with 
the word white or the letter W. 

9 

I FPN: See Section 250-126 for identification of wiring de- 
vice equipment grounding conductor terminals. 

(c) Screw Shells. For devices with screw shells, the termi- 
nal for the grounded conductor shall be the one connected 
to the screw shell. 

(d) Screw Shell Devices with Leads. For screw shell de- 
vices with attached leads, the conductor attached to the screw 
shell shall have a white or natural gray finish. The outer 
finish of the other conductor shall be of a solid color that 
will not be confused with the white or natural gray finish 
used to identify the grounded conductor. 

(e) Appliances. Appliances that have a single-pole switch 
or a single-pole overcurrent device in the line or any line- 
connected screw shell lampholders, and that are to be con- 



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NATIONAL ELECTRICAL CODE 



ARTICLE 210 — BRANCH CIRCUITS 



70-37 



nected by (1) a permanent wiring method or (2) field-in- 
stalled attachment plugs and cords with three or more wires 
(including the equipment grounding conductor), shall have 
means to identify the terminal for the grounded circuit con- 
ductor (if any). 

200-11. Polarity of Connections. No grounded conductor 
shall be attached to any terminal or lead so as to reverse the 
designated polarity. 

Article 210 — Branch Circuits 

A. General Provisions 

210-1. Scope. This article covers branch circuits except for 
branch circuits that supply only motor loads, which are 
covered in Article 430. Provisions of this article and Article 
430 apply to branch circuits with combination loads. 

f 

210-2. Other Articles for Specific-Purpose Branch Cir- 
cuits. Branch circuits shall comply with this article and also 
with the applicable provisions of other articles of this Code. 
The provisions for branch circuits supplying equipment in 
the following list amend or supplement the provisions in 
this article and shall apply to branch circuits referred to 
therein. 



Article 



Fixed outdoor electric deicing and 

snow-melting equipment 
Information technology equipment 
Infrared lamp industrial heating 

equipment 
Induction and dielectric heating 

equipment 
Marinas and boatyards 
Mobile homes, manufactured homes, 

and mobile home parks 
Motion picture and television studios 

and similar locations 
Motors, motor circuits, and 

controllers 
Pipe organs 
Recreational vehicles and 

recreational vehicle parks 
Sound-recording and similar 

equipment 
Switchboards and panelboards 
Theaters, audience areas of motion 

picture and television studios, and 

similar locations 
X-ray equipment 



665 

550 
530 
430 

551 



Section 

426-4 

645-5 

422-48 

424-3 



555-5 



650-7 



640-6 

384-32 

520-41 

520-52 

520-62 

660-2 

517-73 



Article 



Air-conditioning and refrigerating 
equipment 

Busways 

Circuits and equipment operating at 
less than 50 volts 

Central heating equipment other than 
fixed electric space-heating 
equipment 

Class 1, Class 2, and Class 3 remote- 
control, signaling, and power- 
limited circuits 

Closed-loop and programmed power 
distribution 

Cranes and hoists 

Electric signs and outline lighting 

Electric welders 

Elevators, dumbwaiters, escalators, 
moving walks, wheel chairlifts, 
and stairway chair lifts 

Fire alarm systems 

Fixed electric heating equipment for 
pipelines and vessels 

Fixed electric space-heating 
equipment 



720 



725 



780 



630 



760 



Section 

440-6 
440-31 
440-32 
364-9 



422-12 



610-42 
600-6 

620-61 



427-4 
424-3 



210-3. Rating. Branch circuits recognized by this article 
shall be rated in accordance with the maximum permitted 
ampere rating or setting of the overcurrent device. The rating 
for other than individual branch circuits shall be 15, 20, 30, 
40, and 50 amperes. Where conductors of higher ampacity 
are used for any reason, the ampere rating or setting of 
the specified overcurrent device shall determine the circuit 
rating. 

Exception: Multioutlet branch circuits greater than 50 am- 
peres shall be permitted to supply nonlighting outlet loads 
on industrial premises where maintenance and supervision 
indicate that qualified persons will service the equipment. 

210-4. Multiwire Branch Circuits. 

(a) General. Branch circuits recognized by this article shall 
be permitted as multiwire circuits. A multiwire branch circuit 
shall be permitted to be considered as multiple circuits. All 
conductors shall originate from the same panelboard. 

FPN: A 3 -phase, 4- wire, wye-connected power system used 
to supply power to nonlinear loads may' necessitate that 
the power system design allow for the possibility of high 
harmonic neutral currents. 

(b) Dwelling Units. In dwelling units, a multiwire branch 
circuit supplying more than one device or equipment on the 
same yoke shall be provided with a means to disconnect 



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70-38 



ARTICLE 210 — BRANCH CIRCUITS 



simultaneously all ungrounded conductors at the panelboard 
where the branch circuit originated. 

(c) Line-to-Neutral Loads. Multiwire branch circuits shall 
supply only line-to-neutral loads. 

Exception No. 1: A multiwire branch circuit that supplies 
only one utilization equipment. 

Exception No. 2: Where all ungrounded conductors of the 
multiwire branch circuit are opened simultaneously by the 
branch-circuit overcurrent device. 

FPN: See Section 300-13(b) for continuity of grounded con- . 
ductor on multiwire circuits. 

(d) Identification of Ungrounded Conductors. Where 
more than one nominal voltage system exists in a building, 
each ungrounded conductor of a multiwire branch circuit, 
where accessible, shall be identified by phase and system. 
This means of identification shall be permitted to be by 
separate color coding, marking tape, tagging, or other ap- 
proved means and shall be permanently posted at each 
branch-circuit panelboard. 



210-5. Identification for Branch Circuits. 

(a) Grounded Conductor. The grounded conductor of a 
branch circuit shall be identified in accordance with Section 
200-6. 

(b) Equipment Grounding Conductor. The equipment 
grounding conductor shall be identified in accordance with 
Section 250-119. 

210-6. Branch-Circuit Voltage Limitations. 

(a) Occupancy Limitation. In dwelling units and guest 
rooms of hotels, motels, and similar occupancies, the voltage 
shall not exceed 120 volts, nominal, between conductors 
that supply the terminals of the following: 

(1) Lighting fixtures 

(2) Cord- and plug-connected loads 1440 volt-amperes, 
nominal, or less, or less than l A hp 

(b) 120 Volts Between Conductors. Circuits not exceed- 
ing 120 volts, nominal, between conductors shall be permit- 
ted to supply the following: 

(1) The terminals of lampholders applied within their volt- 
age ratings 

(2) Auxiliary equipment of electric-discharge lamps 

(3) Cord- and plug-connected or permanently connected uti- 
lization equipment 

(c) 277 Volts to Ground. Circuits exceeding 120 volts, 
nominal, between conductors and not exceeding 277 volts, 



nominal, to ground shall be permitted to supply the follow- 
ing: 

(1) Listed electric-discharge lighting fixtures 

(2) Listed incandescent lighting fixtures, where supplied at 
120 volts or less from the output of a stepdown autotrans- 
former that is an integral component of the fixture and 
the outer shell terminal is electrically connected to a 
grounded conductor of the branch circuit 

(3) Lighting fixtures equipped with mogul-base screw shell 
lampholders 

(4) Lampholders, other than the screw shell type, applied 
within their voltage ratings 

(5) Auxiliary equipment of electric-discharge lamps 

(6) Cord- and plug-connected or permanently connected uti- 
lization equipment 

(d) 600 Volts Between Conductors. Circuits exceeding 
277 volts, nominal, to ground and not exceeding 600 volts, 
nominal, between conductors shall be permitted to supply 
the following: 

(1) The auxiliary equipment of electric-discharge lamps 
mounted in permanently installed fixtures where the 
fixtures are mounted in accordance with one of the 
following: 

(a) Not less than a height of 22 ft (6.71 m) on poles or 
similar structures for the illumination of outdoor 
areas such as highways, roads, bridges, athletic 
fields, or parking lots 

(b) Not less than a height of 18 ft (5.49 m) on other 
structures such as tunnels 

(2) Cord- and plug-connected or permanently connected 
utilization equipment 

FPN: See Section 410-78 for auxiliary equipment limita- 
tions. 

Exception No. 1 to (b), (c), and (d): For lampholders of 
infrared industrial heating appliances as provided in Section 
422-14. 

Exception No. 2 to (b), (c), and (d): For railway 'properties 
as described in Section 110-19. 

210-7. Receptacles and Cord Connectors. 

(a) Grounding Type. Receptacles installed on 15- and 
20-ampere branch circuits shall be of the grounding type. 
Grounding-type receptacles shall be installed only on circuits 
of the voltage class and current for which they are rated, 
except as provided in Tables 210-21(b)(2) and (b)(3). 

Exception: Nongrounding-type receptacles installed in ac- 
cordance with Section 210-7 (d). 



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ARTICLE 210 — BRANCH CIRCUITS 



70-39 



(b) To Be Grounded. Receptacles and cord connectors 
that have grounding contacts shall have those contacts effec- 
tively grounded. 

Exception No. 1: Receptacles mounted on portable and 
vehicle-mounted generators in accordance with Section 
I 250-34. 

Exception No. 2: Replacement receptacles as permitted by 
Section 2 10-7 (d) 

(c) Methods of Grounding. The grounding contacts of re- 
ceptacles and cord connectors shall be grounded by con- 
nection to the equipment grounding conductor of the circuit 
supplying the receptacle or cord connector. 

FPN: For installation requirements for the reduction of elec- 
I trical noise, see Section 250- 146(d). 

The branch-circuit wiring method shall include or provide 
an equipment grounding conductor to which the grounding 
contacts of the receptacle or cord connector shall be con- 
nected. 

I FPN No. 1: Section 250-1 18 describes acceptable grounding 
means. 

FPN No. 2: For extensions of existing branch circuits, see 
I Section 250-130. 

(d) Replacements. Replacement of receptacles shall com- 
ply with (1), (2), and (3) as applicable. 

(1) Where a grounding means exists in the receptacle 
. enclosure or a grounding conductor is installed in accordance 
I with Section 250- 130(c), grounding-type receptacles shall 

be used and shall be connected to the grounding conductor 
I in accordance with Sections 210-7(c) or 250- 130(c). 

(2) Ground-fault circuit-interrupter protected receptacles 
shall be provided where replacements are made at receptacle 
outlets that are required to be so protected elsewhere in this 
Code. 

(3) Where a grounding means does not exist in the recep- 
tacle enclosure, the installation shall comply with (a), (b), 
or (c). 

(a) A nongrounding-type receptacle(s) shall be permitted to 
be replaced with another nongrounding-type recepta- 
cle^). . 

(b) A nongrounding-type receptacle(s) shall be permitted 
to be replaced with a ground-fault circuit interrupter- 
type of receptacle(s). These receptacles shall be marked 
"No Equipment Ground." An equipment grounding 
conductor shall not be connected from the ground-fault 
circuit interrupter-type receptacle to any outlet supplied 
from the ground-fault circuit interrupter receptacle. 

(c) A nongrounding-type receptacle(s) shall be permitted to 



be replaced with a grounding-type receptacle(s) where 
supplied through a ground-fault circuit interrupter. 
Grounding-type receptacles supplied through the 
ground-fault circuit interrupter shall be marked "GFCI 
Protected" and "No Equipment Ground." An equipment 
grounding conductor shall not be connected between the 
grounding-type receptacles. 

(e) Cord- and Plug-Connected Equipment. The instal- 
lation of grounding-type receptacles shall not be used as a 
requirement that all cord- and plug-connected equipment be 
of the grounded type. 

I FPN: See Section 250-114 for types of cord- and plug- 
connected equipment to be grounded. 

(f) Noninterchangeable Types. Receptacles connected to 
circuits that have different voltages, frequencies, or types 
of current (ac or dc) on the same premises shall be of such 
design that the attachment plugs used on these circuits are 
not interchangeable. 

210-8. Ground-Fault Circuit-Interrupter Protection for 
Personnel. 

FPN: See Section 215-9 for ground-fault circuit-interrupter 
protection for personnel on feeders. 

(a) Dwelling Units. All 125-volt, single-phase, 15- and 20- 
ampere receptacles installed in the locations specified below 
shall have ground-fault circuit-interrupter protection for per- 
sonnel. 

(1) Bathrooms. 

(2) Garages, and also accessory buildings that have a floor 
located at or below grade level not intended as habitable 
rooms and limited to storage areas, work areas, and 
areas of similar use. 

Exception No. 1 : Receptacles that are not readily accessible. 

Exception No. 2: A single receptacle or a duplex receptacle 
for two appliances located within dedicated space for each 
appliance that, in normal use, is not easily moved from one 
place to another, and that is cord- and plug-connected in 
accordance with Section 400-7 (a)(6), (a)(7), or (a)(8). 

Receptacles installed under the exceptions to Section 210- 
8(a)(2) shall not be considered as meeting the requirements 
of Section 210-52(g). 

(3) Outdoors. 

Exception: Receptacles that are not readily accessible and 
are supplied by a dedicated branch circuit for electric snow- 
melting or deicing equipment shall be permitted to be in- 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-40 



ARTICLE 210 — BRANCH CIRCUITS 



stalled in accordance with the applicable provisions of Arti- 
cle 426. 

(4) Crawl spaces. Where the crawl space is at or below 
grade level. 

(5) Unfinished basements. For purposes of this section, un- 
finished basements are defined as portions or areas of the 
basement not intended as habitable rooms and limited to 
storage areas, work areas, and the like. 

Exception No. 1 : Receptacles that are not readily accessible. 

Exception No. 2: A single receptacle or a duplex receptacle 
for two appliances located within dedicated space for each 
appliance that, in normal use, is not easily moved from one 
place to another, and that is cord- and plug-connected in 
accordance with Section 400-7(a)(6), (a)(7), or (a)(8). 

Receptacles installed under the exceptions to Section 210- 
8(a)(5) shall not be considered as meeting the requirements 
of Section 210-52(g). 

(6) Kitchens. Where the receptacles are installed to serve 
the countertop surfaces. 

(7) Wet bar sinks. Where the receptacles are installed to 
serve the countertop surfaces and are located within 6 
ft (1.83 m) of the outside edge of the wet bar sink. 
Receptacle outlets shall not be installed in a face-up 
position in the work surfaces or countertops. 

(b) Other than Dwelling Units. All 125 -volt, single- 
phase, 15- and 20-ampere receptacles installed in the loca- 
tions specified below shall have ground-fault circuit-inter- 
rupter protection for personnel. 

(1) Bathrooms 

(2) Rooftops 

Exception: Receptacles that are not readily accessible and 
are supplied from a dedicated branch circuit for electric 
snow-melting or deicing equipment shall be permitted to be 
installed in accordance with the applicable provisions of 
Article 426. 

210-9. Circuits Derived from Autotransformers. Branch 
circuits shall not be derived from autotransformers unless the 
circuit supplied has a grounded conductor that is electrically 
connected to a grounded conductor of the system supplying 
the autotransformer. 

I Exception No. 1: An autotransformer shall be permitted 
without the connection to a grounded conductor where trans- 
forming from a nominal 208 volts to a nominal 240-volt 
supply or similarly from 240 volts to 208 volts. 



Exception No. 2: In industrial occupancies, where condi- 
tions of maintenance and supervision ensure that only qual- 
ified persons will service the installation, autotransformers 
shall be permitted to supply nominal 600-volt loads from 
nominal 480-volt systems, and 480-volt loads from nominal 
600-volt systems, without the connection to a similar 
grounded conductor. 

210-10. Ungrounded Conductors Tapped from 
Grounded Systems. Two-wire dc circuits and ac circuits 
of two or more ungrounded conductors shall be permitted 
to be tapped from the ungrounded conductors of circuits 
that have a grounded neutral conductor. Switching devices 
in each tapped circuit shall have a pole in each ungrounded 
conductor. All poles of multipole switching devices shall 
manually switch together where such switching devices also 
serve as a disconnecting means as required by the following: 

(1) Section 410-48 for double-pole switched lampholders 

(2) Section 410-54(b) for electric-discharge lamp auxiliary 
equipment switching devices 

(3) Section 422-3 1(b) for an appliance 

(4) Section 424-20 for a fixed electric space-heating unit 

(5) Section 426-51 for electric deicing and snow-melting 
equipment 

(6) Section 430-85 for a motor controller 

(7) Section 430-103 for a motor 

210-11. Branch Circuits Required. Branch circuits for 
lighting and for appliances, including motor-operated appli- 
ances, shall be provided to supply the loads computed in 
accordance with Section 220-3. In addition, branch circuits 
shall be provided for specific loads not covered by Section 
220-3 where required elsewhere in this Code and for dwell- 
ing unit loads as specified in (c). 

(a) Number of Branch Circuits. The minimum number 
of branch circuits shall be determined from the total com- 
puted load and the size or rating of the circuits used. In all 
installations, the number of circuits shall be sufficient to 
supply the load served. In no case shall the load on any 
circuit exceed the maximum specified by Section 220-4. 

(b) Load Evenly Proportioned Among Branch Cir- 
cuits. Where the load is computed on a volt-amperes/square 
foot (0.093 m 2 ) basis, the wiring system up to and including 
the branch-circuit panelboard(s) shall be provided to serve 
not less than the calculated load. This load shall be evenly 
proportioned among multioutlet branch circuits within the 
panelboard(s). Branch-circuit overcurrent devices and cir- 
cuits need only be installed to serve the connected load. 

(c) Dwelling Units. 

(1) Small- Appliance Branch Circuits. In addition to 
the number of branch circuits required by other parts of 



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ARTICLE 210 — BRANCH CIRCUITS 



70-41 



this section, two or more 20-ampere small-appliance branch 
circuits shall be provided for all receptacle outlets specified 
by Section 210-52(b). 

(2) Laundry Branch Circuits. In addition to the num- 
ber of branch circuits required by other parts of this section, 
at least one additional 20-ampere branch circuit shall be 
provided to supply the laundry receptacle outlet(s) required 
by Section 210-52(f). This circuit shall have no other outlets. 

(3) Bathroom Branch Circuits. In addition to the num- 
ber of branch circuits required by other parts of this section, 
at least one 20-ampere branch circuit shall be provided to 
supply the bathroom receptacle outlet(s). Such circuits shall 
have no other outlets. 

Exception: Where the 20-ampere circuit supplies a single 
bathroom, outlets for other equipment within the same bath- 
room shall be permitted to be supplied in accordance with 
Section 210-23(a). 

FPN: See Examples Dl(a), Dl(b), D2(b), and D4(a) in Ap- 
pendix D. 

210-12. Arc-Fault Circuit-Interrupter Protection. 

(a) Definition. An arc-fault circuit interrupter is a device 
intended to provide protection from the effects of arc faults 
by recognizing characteristics unique to arcing and by func- 
tioning to de-energize the circuit when an arc fault is de- 
tected. 

(b) Dwelling Unit Bedrooms. All branch circuits that sup- 
ply 125-volt, single-phase, 15- and 20-ampere receptacle 
outlets installed in dwelling unit bedrooms shall be protected 
by an arc-fault circuit interrupter(s). This requirement shall 
become effective January 1, 2002. 

B. Branch-Circuit Ratings 

210-19. Conductors — Minimum Ampacity and Size; 

(a) General. Branch-circuit conductors shall have an am- 
pacity not less than the maximum load to be served. Where 
a branch circuit supplies continuous loads or any combina- 
tion of continuous and noncontinuous loads, the minimum 
branch-circuit conductor size, before the application of any 
adjustment or correction factors, shall have an allowable 
ampacity equal to or greater than the noncontinuous load 
plus 125 percent of the continuous load. 

Exception: Where the assembly, including the overcurrent 
devices protecting the branch circuit(s), is listed for opera- 
tion at 100 percent of its rating, the ampacity of the branch 
circuit conductors shall be permitted to be not less than the 
sum of the continuous load plus the noncontinuous load. 

FPN No. 1: See Section 310-15 for ampacity ratings of 
conductors. 



FPN No. 2: See Part B of Article 430 for minimum rating 
of motor branch-circuit conductors. 

FPN No. 3: See Section 310-10 for temperature limitation 
of conductors. 

FPN No. 4: Conductors for branch circuits as defined in 
Article 100, sized to prevent a voltage drop exceeding 3 
percent at the farthest outlet of power, heating, and lighting 
loads, or combinations of such loads, and where the maxi- 
mum total voltage drop on both feeders and branch circuits 
to thefarthest outlet does not exceed 5 percent, will provide 
reasonable efficiency of operation. See Section 215-2 for 
voltage drop on feeder conductors. 

(b) Multioutlet Branch Circuits. Conductors of branch 
circuits supplying more than one receptacle for cord- and 
plug-connected portable loads shall have an ampacity of not 
less than the rating of the branch circuit. 

(c) Household Ranges and Cooking Appliances. Branch- 
circuit conductors supplying household ranges, wall- 
mounted ovens, counter-mounted cooking units, and other 
household cooking appliances shall have an ampacity not 
less than the rating of the branch circuit and not less than 
the maximum load to be served. For ranges of 8 3 /4 kW or 
more rating, the minimum branch-circuit rating shall be 40 
amperes. 

Exception No. 1: Tap conductors supplying electric ranges, 
wall-mounted electric ovens, and counter-mounted electric 
cooking units from a 50-ampere branch circuit shall have 
an ampacity of not less than 20 and shall be sufficient for 
the load to be served. The taps shall not be longer than 
necessary for servicing the appliance. 

Exception No. 2: The neutral conductor of a 3-wire branch 
circuit supplying a household electric range, a wall-mounted 
oven, or a counter-mounted cooking unit shall be permitted 
to be smaller than the ungrounded conductors where the 
maximum demand of a range of 8 3 A kW or more rating has 
been computed according to Column A of Table 220-19, but 
shall have an ampacity of not less than 70 percent of the 
branch-circuit rating and shall not be smaller than No. 10. 

(d) Other Loads. Branch-circuit Conductors that supply 
loads other than those specified in Section 210-2 and other 
than cooking appliances as covered above shall have an 
ampacity sufficient for the loads served and shall not be 
smaller than No. 14. 

Exception No. 1: Tap conductors for such loads shall have 
an ampacity of not less than 15 for circuits rated less than 
40 amperes and of not less than 20 for circuits rated at 40 
or 50 amperes and only where these tap conductors supply 
any of the following loads: 

(a) Individual lampholders or fixtures with taps extending 
not longer than 18 in. (457 mm) beyond any portion of 
the lampholder or fixture 



NATIONAL ELECTRICAL CODE 



L999 Edition 



70-42 



ARTICLE 210 — BRANCH CIRCUITS 



(b) A fixture having tap conductors as provided in Section 
410-67 

(c) Individual outlets, other than receptacle outlets, with 
taps not over 18 in. (457 mm) long 

(d) Infrared lamp industrial heating appliances 

(e) Nonhealing leads of deicing and snow-melting cables 
and mats 

Exception No. 2: Fixture wires and flexible cords shall be 
permitted to be smaller than No. 14 as permitted by Section 
240-4. 

210-20. Overcurrent Protection. Branch-circuit conduc- 
tors and equipment shall be protected by overcurrent pro- 
tective devices that have a rating or setting that complies 
with (a) through (d). 

(a) Continuous and Noncontinuous Loads. Where a 
branch circuit supplies continuous loads or any combination 
of continuous and noncontinuous loads, the rating of the 
overcurrent device shall not be less than the noncontinuous 
load plus 125 percent of the continuous load. 

Exception: Where the assembly, including the overcurrent 
devices protecting the branch circuit(s), is listed for opera- 
tion at 100 percent of its rating, the ampere rating of the 
overcurrent device shall be permitted to be not less than the 
sum of the continuous load plus the noncontinuous load 

(b) Conductor Protection. Conductors shall be protected 
in accordance with Section 240-3. 

Exception No. 1: Tap conductors as permitted in Section 
2 10- 19(d) shall be permitted to be protected by the branch- 
circuit overcurrent device. 

Exception No. 2: Fixture wires and flexible cords shall be 
permitted to be protected in accordance with Section 240-4. 

(c) Equipment. The rating or setting of the overcurrent 
protective device shall not exceed that specified in the appli- 
cable articles referenced in Section 240-2 for equipment. 

(d) Outlet Devices. The rating or setting shall not exceed 
that specified in Section 210-21 for outlet devices. 

210-21. Outlet Devices. Outlet devices shall have an am- 
pere rating that is not less than the load to be served and 
shall comply with (a) and (b). 

(a) Lampholders. Where connected to a branch circuit 
having a rating in excess of 20 amperes, lampholders shall 
be of the heavy-duty type. A heavy-duty lampholder shall 
have a rating of not less than 660 watts if of the admedium 
type and not less than 750 watts if of any other type. 



(b) Receptacles. 

(1) A single receptacle installed on an individual branch 
circuit shall have an ampere rating of not less than that of 
the branch circuit. 

Exception No. 1: Where installed in accordance with Sec- 
tion 430-81 (c). 

Exception No. 2: A receptacle installed exclusively for the 
use of a cord- and plug-connected arc welder shall be per- 
mitted to have an ampere rating not less than the minimum 
branch-circuit conductor ampacity determined by Section 
630-ll(a) for arc welders. 

FPN: See definition of Receptacle in Article 100. 

(2) Where connected to a branch circuit supplying two 
or more receptacles or outlets, a receptacle shall not supply 
a total cord- and plug-connected load in excess of the maxi- 
mum specified in Table 2 10-2 1(b)(2). 

Table 210-21(b)(2). Maximum Cord- and Plug-Connected 
Load to Receptacle 



Circuit Rating 
(Amperes) 



Receptacle Rating 
(Amperes) 



Maximum Load 
(Amperes) 



15 or 20 


15 


20 


20 


30 


30 



12 
16 

24 



(3) Where connected to a branch circuit supplying two 
or more receptacles or outlets, receptacle ratings shall con- 
form to the values listed in Table 210-21 (b)(3), or, where 
larger than 50 amperes, the receptacle rating shall not be 
less than the branch-circuit rating. 

Exception: Receptacles for one or more cord- and plug- 
connected arc welders shall be permitted to have ampere 
ratings not less than the minimum branch-circuit conductor 
ampacity permitted by Sections 630- 11 (a) or (b) as applica- 
ble for arc welders. 



Table 210-21(b)(3). Receptacle Ratings for Various Size 
Circuits 



Circuit Rating 


Receptacle Rating 




(Amperes) 


(Amperes) 




15 


Not over 15 




20 


15 or 20 




30 


30 




40 


40 or 50 




50 


50 





1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 210 — BRANCH CIRCUITS 



70-43 



(4) The ampere rating of a range receptacle shall be 
permitted to be based on a single range demand load as 
specified in Table 220-19. 

210-23. Permissible Loads. In no case shall the load ex- 
ceed the branch-circuit ampere rating. An individual branch 
circuit shall be permitted to supply any load for which it is 
rated. A branch circuit supplying two or more outlets or 
receptacles shall supply only the loads specified according 
to its size as specified in (a) through (d) and as summarized 
in Section 210-24 and Table 210-24. 

(a) 15- and 20-Ampere Branch Circuits. A 15- or 20- 

ampere branch circuit shall be permitted to supply lighting 
units or other utilization equipment, or a combination of 
both. The rating of any one cord- and plug-connected utili- 
zation equipment shall not exceed 80 percent of the branch- 
circuit ampere rating. The total rating of utilization equip- 
ment fastened in place, other than lighting fixtures, shall not 
exceed 50 percent of the branch-circuit ampere rating where 
lighting units, cord- and plug-connected utilization equip- 
ment not fastened in place, or both, are also supplied. 

Exception: The small appliance branch circuits, laundry 
branch circuits, and bathroom branch circuits required in 
a dwelling unit(s) by Sections 210-ll(c)(l), (2), and (3) shall 
supply only the receptacle outlets specified in that section. 

(b) 30-Ampere Branch Circuits. A 30-ampere branch cir- 
cuit shall be permitted to supply fixed lighting units with 
heavy-duty lampholders in other than a dwelling unit(s) or 
utilization equipment in any occupancy. A rating of any one 
cord- and plug-connected utilization equipment shall not 
exceed- 80 percent of the branch-circuit ampere rating. 



(c) 40- and 50-Ampere Branch Circuits. A 40- or 50- 

ampere branch circuit shall be permitted to supply cooking 
appliances that are fastened in place in any occupancy. In 
other than dwelling units, such circuits shall be permitted 
to supply fixed lighting units with heavy-duty lampholders, 
infrared heating units, or other utilization equipment. 

(d) Branch Circuits Larger than 50 Amperes. Branch 
circuits larger than 50 amperes shall supply only nonlighting 
outlet loads. 

210-24. Branch-Circuit Requirements — Summary. 

The requirements for circuits that have two or more outlets 
or receptacles, other than the receptacle circuits of 
Sections 210-1 1(c)(1) and (2) as specifically provided for 
above, are summarized in Table 210-24. 

210-25. Common Area Branch Circuits. Branch circuits 
in dwelling units shall supply only loads within that dwelling 
unit or loads associated only with that dwelling unit. Branch 
circuits required for the purpose of lighting, central alarm, 
signal, communications, or other needs for public or com- 
mon areas of a two-family or multifamily dwelling shall 
not be supplied from equipment that supplies an individual 
dwelling unit. 

C. Required Outlets 

210-50. General. Receptacle outlets shall be installed as 
specified in Sections 210-52 through 210-63. 

(a) Cord Pendants. A cord connector that is supported by 
a permanently installed cord pendant shall be considered a 
receptacle outlet. 



Table 210-24. Summary of Branch-Circuit Requirements 



Circuit Rating 



15 A 



20 A 



30 A 



40 A 



50 A 



Conductors (rnin. size): 










Circuit wires 1 




14 


12 


10 


Taps 




14 


14 


14 


Fixture wires and cords - 


- See Section 240-4 









12 



'These gauges are for copper conductors. 

2 Fpr receptacle rating of cord-connected electric-discharge lighting fixtures, see Section 410-30(c). 



6 
12 



Overcurrent Protection 


15 A 


20 A 


30 A 


40 A 


50 A 


Outlet Devices: 

Lampholders permitted 
Receptacle rating 2 


Any type 
15 max. A 


Any type 
15 or 20 A 


Heavy duty 
30 A 


Heavy duty 
40 or 50 A 


Heavy duty 
50 A 


Maximum Load 


15 A 


20 A 


30 A 


40 A 


50 A 


Permissible load 


See Section 
210-23(a) 


See Section 
210-23(a) 


See Section 
210-23(b) 


See Section 
210-23(c) 


See Section 
210-23(c) 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-44 



ARTICLE 210 — BRANCH CIRCUITS 



(b) Cord Connections. A receptacle outlet shall be in- 
stalled wherever flexible cords with attachment plugs are 
used. Where flexible cords are permitted to be permanently 
connected, receptacles shall be permitted to be omitted for 
such cords. 

(c) Appliance Outlets. Appliance receptacle outlets in- 
stalled in a dwelling unit for specific appliances, such as 
laundry equipment, shall be installed within 6 ft (1.83 m) 
of the intended location of the appliance. 

210-52. Dwelling Unit Receptacle Outlets. Receptacle 
outlets required by this section shall be in addition to any 
receptacle that is part of a lighting fixture or appliance, 
located within cabinets or cupboards, or located more than 
5 J /2 ft (1.68 m) above the floor. 

Permanently installed electric baseboard heaters equipped 
with factory-installed receptacle outlets or outlets provided 
as a separate assembly by the manufacturer shall be permit- 
ted as the required outlet or outlets for the wall space utilized 
by such permanently installed heaters. Such receptacle out- 
lets shall not be connected to the heater circuits. 

FPN: Listed baseboard heaters include instructions that may 
not permit their installation below receptacle outlets. 

(a) General Provisions. In every kitchen, family room, 
dining room, living room, parlor, library, den, sunroom, bed- 
room, recreation room, or similar room or area of dwelling 
units, receptacle outlets shall be installed in accordance with 
the general provisions specified in (1) through (3). 

(1) Spacing. Receptacles shall be installed so that no 
point along the floor line in any wall space is more than 6 
ft (1.83 m), measured horizontally, from an outlet in that 
space. Receptacle outlets shall, insofar as practicable, be 
spaced equal distances apart. 

(2) Wall Space. As used in this section, a wall space 
shall include the following: 

(a) Any space 2 ft (610 mm) or more in width (including 
space measured around corners) and unbroken along the 
floor line by doorways, fireplaces, and similar openings 

(b) The space occupied by fixed panels in exterior walls, 
excluding sliding panels 

(c) The space afforded by fixed room dividers such as free- 
standing bar-type counters or railings 

(3) Floor Receptacles. Receptacle outlets in floors shall 
not be counted as part of the required number of receptacle 
outlets unless located within 18 in. (457 mm) of the wall. 

(b) Small Appliances. 

(1) In the kitchen, pantry, breakfast room, dining room, 
or similar area of a dwelling unit, the two or more 20-ampere 



small-appliance branch circuits required by Section 210- 
1 1(c)(1) shall serve all receptacle outlets covered by Sections 
210-52(a) and (c) and receptacle outlets for refrigeration 
equipment. 

Exception No. 1: In addition to the required receptacles 
specified by Section 210-52, switched receptacles supplied 
from a general-purpose branch circuit as defined in Section 
210-70(a)(l), Exception No. 1, shall be permitted. 

Exception No. 2: The receptacle outlet for refrigeration ' 
equipment shall be permitted to be supplied from an individ- 
ual branch circuit rated 15 amperes or greater 

(2) The two or more small-appliance branch circuits 
specified in (b)(1) shall have no other outlets. 

Exception No. 1: A receptacle installed solely for the elec- 
trical supply to and support of an electric clock in any of 
the rooms specified above. 

Exception No. 2: Receptacles installed to provide power for 
supplemental equipment and lighting on gas-fired ranges, 
ovens, or counter-mounted cooking units. 

(3) Receptacles installed in a kitchen to serve countertop 
surfaces shall be supplied by not less than two small-appli- 
ance branch circuits, either or both of which shall also be 
permitted to supply receptacle outlets in the same kitchen 
and in other rooms specified in Section 210-52(b)(l). Addi- 
tional small-appliance branch circuits shall be permitted to 
supply receptacle outlets in the kitchen and other rooms 
specified in Section 210-52(b)(l). No small-appliance 
branch circuit shall serve more than one kitchen.. 

(c) Countertops. In kitchens and dining rooms of dwelling 
units, receptacle outlets for counter spaces shall be installed 
in accordance with (1) through (5). 

(1) Wall Counter Spaces. A receptacle outlet shall be 
installed at each wall counter space that is 12 in. (305 mm) 
or wider. Receptacle outlets shall be installed so that no 
point along the wall line is more than 24 in. (610 mm), 
measured horizontally from a receptacle outlet in that space. 

(2) Island Counter Spaces. At least one receptacle out- 
let shall be installed at each island counter space with a 
long dimension of 24 in. (610 mm) or greater and a short 
dimension of 12 in. (305 mm) or greater. 

(3) Peninsular Counter Spaces. At least one receptacle 
outlet shall be installed at each peninsular counter space 
with a long dimension of 24 in. (610 mm) or greater and a 
short dimension of 12 in. (305 mm) or greater. A peninsular 
countertop is measured from the connecting edge. 

(4) Separate Spaces. Countertop spaces separated by 
range tops, refrigerators, or sinks shall be considered as 



1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 210 — BRANCH CIRCUITS 



70-45 



separate countertop spaces in applying the requirements of 
(1), (2), and (3). 

(5) Receptacle Outlet Location. Receptacle outlets 
shall be located above, but not more than 18 in. (458 mm) 
above the countertop. Receptacle outlets shall not be in- 
stalled in a face-up position in the work surfaces or coun- 
tertops. Receptacle outlets rendered not readily accessible 
by appliances fastened in place or appliances occupying 
dedicated space shall not be considered as these required 
outlets. 

Exception: To comply with the conditions as specified in 
(a) or (b), receptacle outlets shall be permitted to be mounted 
not more than 12 in. (305 mm) below the countertop. Recep- 
tacles mounted below the countertop in accordance with 
this exception shall not be located where the countertop 
extends more than 6 in. (153 mm) beyond its support base. 

(a) Construction for the physically impaired 

(b) On island and peninsular countertops where the coun- 
tertop is flat across its entire surface (no backsplashes, 
dividers, etc.) and there are no means to mount a recep- 
tacle within 18 in. (458 mm) above the countertop, such 
as an overhead cabinet 

(d) Bathrooms. In dwelling units, at least one wall recep- 
tacle outlet shall be installed in bathrooms within 36 in. (914 
mm) of the outside edge of each basin. The receptacle outlet 
shall be located on a wall that is adjacent to the basin loca- 
tion. See Section 210-8(a)(l). 

Receptacle outlets shall not be installed in a face-up posi- 
tion in the work surfaces or countertops in a bathroom basin 
location. 

(e) Outdoor Outlets. For a one-family dwelling and each 
unit of a two-family dwelling that is at grade level, at least 
one receptacle outlet accessible at grade level and not more 
than 6'/2 ft (1.98 m) above grade shall be installed at the 
front and back of the dwelling. See Section 210-8(a)(3). 

(f) Laundry Areas. In dwelling units, at least one recepta- 
cle outlet shall be installed for the laundry. 

Exception No. 1: In a dwelling unit that is an apartment or 
living area in a multifamily building where laundry facilities 
are provided on the premises that are available to all building 
occupants, a laundry receptacle shall not be required. 

Exception No. 2: In other than one-family dwellings where 
laundry facilities are not to be installed or permitted, a 
laundry receptacle shall not be required. 

(g) Basements and Garages. For a one-family dwelling, 
at least one receptacle outlet, in addition to any provided 
for laundry equipment, shall be installed in each basement 
and in each attached garage, and in each detached garage 
with electric power. See Sections 210-8(a)(2) and (a)(5). 



Where a portion of the basement is finished into a habitable 
room(s), the receptacle outlet required by this section shall 
be installed in the unfinished portion. 

(h) Hallways. In dwelling units, hallways of 10 ft (3.05 
m) or more in length shall have at least one receptacle outlet. 
As used in this subsection, the hall length shall be consid- 
ered the length along the centerline of the hall without pass- 
ing through a doorway. 

210-60. Guest Rooms. 

(a) General. Guest rooms in hotels, motels, and similar 
occupancies shall have receptacle outlets installed in accor- 
dance with Section 210-52. See Section 210-8(b)(l). 

(b) Receptacle Placement. In applying the provisions of 
Section 210-52(a), the total number of receptacle outlets 
shall not be less than the minimum number that would com- 
ply with the provisions of that section. These receptacle 
outlets shall be permitted to be located conveniently for 
permanent furniture layout. At least two receptacle outlets 
shall be readily accessible. Where receptacles are installed 
behind the bed, the receptacle shall be located to prevent 
the bed from contacting any attachment plug that may be 
installed, or the receptacle shall be provided with a suitable 
guard. 

210-62. Show Windows. At least one receptacle outlet 
shall be installed directly above a show window for each 
12 linear ft (3.66 m) or major fraction thereof of show 
window area measured horizontally at its maximum width. 

210-63. Heating, Air-Conditioning, and Refrigeration 
Equipment Outlet. A 125 -volt, single-phase, 15- or 20- 
arripere-rated receptacle outlet shall be installed at an acces- 
sible location for the servicing of heating, air-conditioning, 
and refrigeration equipment on rooftops and in attics and 
crawl spaces. The receptacle shall be located on the same 
level and within 25 ft (7.62 m) of the heating, air-condition- 
ing, and refrigeration equipment. The receptacle outlet shall 
not be connected to the load side of the equipment discon- 
necting means. 

Exception: Rooftop equipment on one- and two-family 
dwellings. 

FPN: See Section 210-8 for ground-fault circuit-interrupter 
requirements. 

210-70. Lighting Outlets Required. Lighting outlets shall 
be installed where specified in (a), (b), and (c). 

(a) Dwelling Units. In dwelling units, lighting outlets shall 
be installed in accordance with (1), (2), and (3). 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-46 



ARTICLE 215 — FEEDERS 



(1) Habitable Rooms. At least one wall switch- 
controlled lighting outlet shall be installed in every habitable 
room and bathroom. 

Exception No. 1: In other than kitchens and bathrooms, one 
or more receptacles controlled by a wall switch shall be 
permitted in lieu of lighting outlets. 

Exception No. 2: Lighting outlets shall be permitted to be 
controlled by occupancy sensors that are (I) in addition to 
wall switches or (2) located at a customary wall switch 
location and equipped with a manual override that will allow 
the sensor to function as a wall switch. 

(2) Additional Locations. At least one wall switch- 
controlled lighting outlet shall be installed in hallways, stair- 
ways, attached garages, and detached garages with electric 
power; and to provide illumination on the exterior side of 
outdoor entrances or exits with grade level access. A vehicle 
door in a garage shall not be considered as an outdoor 
entrance or exit. Where lighting outlets are installed in inte- 
rior stairways, there shall be a wall switch at each floor level 
to control the lighting outlet where the difference between 
floor levels is six steps or more. 

Exception: In hallways, stairways, and at outdoor entranc- 
es, remote, central, or automatic control of lighting shall be 
permitted. 

(3) Storage or Equipment Spaces. For attics, under- 
floor spaces, utility rooms, and basements, at least one light- 
ing outlet containing a switch or controlled by a wall switch 
shall be installed where these spaces are used for storage or 
contain equipment requiring servicing. At least one point of 
control shall be at the usual point of entry to these spaces. 
The lighting outlet shall be provided at or near the equipment 
requiring servicing. 

(b) Guest Rooms. At least one wall switch-controlled 
lighting outlet or wall switch-controlled receptacle shall be 
installed in guest rooms in hotels, motels, or similar occu- 
pancies. 

(c) Other Locations. . For attics and underfloor spaces con- 
taining equipment requiring servicing, such as heating, air- 
conditioning, and refrigeration equipment, at least one 
lighting outlet containing a switch or controlled by a wall 
switch shall be installed in such spaces. At least one point 
of control shall be at the usual point of entry to these spaces. 
The lighting outlet shall be provided at or near the equipment 
requiring servicing. 

Article 215 — Feeders 

215-1. Scope. This article covers the installation require- 
ments, overcurrent protection requirements, minimum size, 



and ampacity of conductors for feeders supplying branch- 
circuit loads as computed in accordance with Article 220. 

Exception: Feeders for electrolytic cells as covered in Sec- 
tion 668-3 (c)(1) and (4). 

215-2. Minimum Rating and Size. 

(a) General. Feeder conductors shall have an ampacity not 
less than required to supply the load as computed in Parts 
B, C, and D of Article 220. The minimum feeder-circuit 
conductor size, before the application of any adjustment or 
correction factors, shall have an allowable ampacity equal 
to or greater than the noncontinuous load plus 125 percent 
of the continuous load. 

Exception: Where the assembly, including the overcurrent 
devices protecting the feeder(s), is listed for operation at 
100 percent of its rating, the ampacity of the feeder conduc- 
tors shall be permitted to be not less than the sum of the 
continuous load plus the noncontinuous load. 

Additional minimum sizes shall be as specified in (b), 
(c), and (d) under the conditions stipulated. 

(b) For Specified Circuits. The ampacity of feeder con- 
ductors shall not v be less than 30 amperes where the load 
supplied consists of any of the following number and types 
of circuits: 

(1) Two or more 2- wire branch circuits supplied by a 2- 
wire feeder 

(2) More than two 2-wire branch circuits supplied by a 
3 -wire feeder 

(3) Two or more 3-wire branch circuits supplied by a 3- 
wire feeder 

(4) Two or more 4-wire branch circuits supplied by a 
3-phase, 4-wire feeder 

(c) Ampacity Relative to Service-Entrance Conductors. 

The feeder conductor ampacity shall not be less than that of 
the service-entrance conductors where the feeder conductors 
carry the total load supplied by service-entrance conductors 
with an ampacity of 55 amperes or less. 

(d) Individual Dwelling Unit or Mobile Home Conduc- 
tors. Feeder conductors for individual dwelling units or 
mobile homes need not be larger than service-entrance con- 
ductors. Section 310-15(b)(6) shall be permitted to be used 
for conductor size. 

FPN No. 1 : See Examples Dl through D10 in Appendix D. 

FPN No. 2: Conductors for feeders as defined in Article 
100, sized to prevent a voltage drop exceeding 3 percent at 
the farthest outlet of power, heating, and lighting loads, or 
combinations of such loads, and where the maximum total 



1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 215 — FEEDERS 



70-47 



voltage drop on both feeders and branch circuits to the 
farthest outlet does not exceed 5 percent, will provide reason- 
able efficiency of operation. 

FPN No. 3: See Section 210-19(a), FPN No. 4, for voltage 
drop for branch circuits. 

215-3. Overcurrent Protection. Feeders shall be protected 
against overcurrent in accordance with the provisions of Part 
A of Article 240. Where a feeder supplies continuous loads 
or any combination of continuous and noncontinuous loads, 
the rating of the overcurrent device shall not be less than 
the noncontinuous load plus 125 percent of the continuous 
load. 

Exception: Where the assembly, including the overcurrent 
devices protecting the feeder(s), is listed for operation at 
100 percent of its rating, the ampere rating of the overcurrent 
device shall be permitted to be not less than the sum of the 
continuous load plus the noncontinuous load. 

215-4. Feeders with Common Neutral. 

(a) Feeders with Common Neutral. Feeders containing a 
common neutral shall be permitted to supply two or three 
sets of 3-wire feeders, or two sets of 4- wire or 5-wire feeders. 

(b) In Metal Raceway or Enclosure. Where installed in 
a metal raceway or other metal enclosure, all conductors of 
all feeders using a common neutral shall be enclosed within 
the same raceway or other enclosure as required in Section 
300-20. 

215-5. Diagrams of Feeders. If required by the authority 
having jurisdiction, a diagram showing feeder details shall 
be provided prior to the installation of the feeders. Such a 
diagram shall show the area in square feet of the building 
or other structure supplied by each feeder, the total connected 
load before applying demand factors, the demand factors 
used, the computed load after applying demand factors, and 
the size and type of conductors to be used. 

215-6. Feeder Conductor Grounding Means. Where a 
feeder supplies branch circuits in which equipment ground- 
ing conductors are required, the feeder shall include or pro- 
vide a grounding means, in accordance with the provisions 
of Section 250-134, to which the equipment grounding con- 
ductors of the branch circuits shall be connected. 

215-7. Ungrounded Conductors Tapped from Grounded 
Systems. Two- wire dc circuits and ac circuits of two or 
more ungrounded conductors shall be permitted to be tapped 
from the ungrounded conductors of circuits having a 
grounded neutral conductor. Switching devices in each tapped 
circuit shall have a pole in each ungrounded conductor. 



215-8. Means of Identifying Conductor with the Higher 
Voltage to Ground. On a 4-wire, delta-connected sec- 
ondary where the midpoint of one phase winding is grounded 
to supply lighting and similar loads, the phase conductor 
having the higher voltage to ground shall be identified by 
an outer finish that is orange in color or by tagging or other 
effective means. Such identification shall be placed at each 
point where a connection is made if the grounded conductor 
is also present. 

215-9. Ground-Fault Circuit-Interrupter Protection for 
Personnel. Feeders supplying 15- and 20-ampere receptacle 
branch circuits shall be permitted to be protected by a 
ground-fault circuit interrupter in lieu of the provisions 
for such interrupters as specified in Section 210-8 and 
Article 305. 

215-10. Ground-Fault Protection of Equipment. Each 
feeder disconnect rated 1000 amperes or more and installed 
on solidly grounded wye electrical systems of more than 
150 volts to ground, but not exceeding 600 volts phase- 
to-phase, shall be provided with ground-fault protection of 
equipment in accordance with the provisions of Section 
230-95. 

Exception No. 1: The provisions of this section shall not 
apply to a disconnecting means for a continuous industrial 
process where a nonorderly shutdown will introduce addi- 
tional or increased hazards. 

Exception No. 2: The provisions of this section shall not 
apply to fire pumps. 

Exception No. 3: The provisions of this section shall not 
apply if ground-fault protection of equipment is provided on 
the supply side of the feeder. 

215-11. Circuits Derived from Autotransformers. Feed- 
ers shall not be derived from autotransformers unless the 
system supplied has a grounded conductor that is electrically 
connected to a grounded conductor of the system supplying 
the autotransformer. 

Exception No. 1: An autotransformer shall be permitted 
without the connection to a grounded conductor where trans- 
forming from a nominal 208 volts to a nominal 240-volt 
supply or similarly from 240 volts to 208 volts. 

Exception No. 2: In industrial occupancies, where condi- 
tions of maintenance and supervision ensure that only qual- 
ified persons service the installation, autotransformers shall 
be permitted to supply nominal 600-volt loads from nominal 
480-volt systems, and 480-volt loads from nominal 600- 
volt systems, without the connection to a similar grounded 
conductor. 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-48 



ARTICLE 220 — BRANCH-CIRCUIT, FEEDER, AND SERVICE CALCULATIONS 



Article 220 — Branch-Circuit, Feeder, and Service 
Calculations 

A. General 

220-1. Scope. This article provides requirements for com- 
puting branch-circuit, feeder, and service loads. 

Exception: Branch-circuit and feeder calculations for elec- 
trolytic cells as covered in Section 668-3(c)(l) and (4). 

220-2. Computations. 

(a) Voltages. Unless other voltages are specified, for pur- 
poses of computing branch-circuit and feeder loads, nominal 
system voltages of 120, 120/240, 208Y/120, 240, 347, 480Y/ 
277, 480, 600Y/347, and 600 volts shall be used. 

(b) Fractions of an Ampere. Except where computations 
result in a fraction of an ampere 0.5 or larger, such fractions 
shall be permitted to be dropped. 

220-3. Computation of Branch Circuit Loads. Branch- 
circuit loads shall be computed as shown in (a) through (c). 

(a) Lighting Load for Specified Occupancies. A unit load 
of not less than that specified in Table 220-3(a) for occupanc- 
ies specified therein shall constitute the minimum lighting 
load for each square foot (0.093 m 2 ) of floor area. The 
floor area for each floor shall be computed from the outside 
dimensions of the building, dwelling unit, or other area 
involved. For dwelling units, the computed floor area shall 
not include open porches, garages, or unused or unfinished 
spaces not adaptable for future use. 

FPN: The unit values herein are based on minimum load 
conditions and 100 percent power factor, and may not pro- 
vide sufficient capacity for the installation contemplated. 

(b) Other Loads — All Occupancies. In all occupancies, 
the minimum load for each outlet for general-use receptacles 
and outlets not used for general illumination shall not be 
less than that computed in (1) through (11), the loads shown 
being based on nominal branch-circuit voltages. 

Exception: The loads of outlets serving switchboards and 
switching frames in telephone exchanges shall be waived 
from the computations. 

(1) Specific Appliances or Loads. An outlet for a spe- 
cific appliance or other load not covered in (2) through (11) 
shall be computed based on the ampere rating of the 
appliance or load served. 

(2) Electric Dryers and Household Electric Cooking 
Appliances. Load computations shall be permitted as spec- 
ified in Section 220-18 for electric dryers and Section 220- 
19 for electric ranges and other cooking appliances. 



Table 220-3(a). General Lighting Loads by Occupancies 





Unit Load per 




Square Foot 


Type of Occupancy 


(Volt-Amperes) 


Armories and auditoriums 


1 


Banks ; 


3'/2 b 


Barber shops and beauty parlors 


3 


Churches 


1. 


Clubs 


2 


Court rooms 


. 2 


Dwelling units 3 


■ 3 


Garages — commercial (storage) 


Vi 


Hospitals 


2 


Hotels and motels, including apartment houses 




without provision for cooking by tenants 3 


2 


Industrial commercial (loft) buildings 


2 


Lodge rooms 


VA 


Office buildings 


3 l /i b 


Restaurants 


2 


Schools 


3 


Stores 


3 


Warehouses (storage) 


% 


In any of the above occupancies except one- 




family dwellings and individual dwelling 




units of two-family and multifamily 




dwellings: 




Assembly halls and auditoriums 


1 


Halls, corridors, closets, stairways 


Vi 


Storage spaces 


Va 



Note: For SI units, 1 ft 2 = 0.093 m 2 . 
I a See Section 220-3(b)(10). 
b In addition, a unit load of 1 volt-ampere per square foot shall be included 
for general-purpose receptacle outlets where the actual number of 
general-purpose receptacle outlets is unknown. 



(3) Motor Loads. Outlets for motor loads shall be com- 
puted in accordance with the requirements in Sections 430- 
22 and 430-24 and Article 440. 

(4) Recessed Lighting Fixtures. An outlet supplying 
recessed lighting fixture(s) shall be computed based on the 
maximum volt-ampere rating of the equipment and lamps 
for which the fixture(s) is rated. 

(5) Heavy Duty Lampholders. Outlets for heavy-duty 
lampholders shall be computed at a minimum of 600 volt- 
amperes. 

(6) Sign and Outline Lighting. Sign and outline light- 
ing outlets shall be computed at a minimum of 1200 volt- 
amperes for each required branch circuit specified in Section 
600-5(a). 

(7) Show Windows. Show windows shall be computed 
in accordance with either (a) or (b). 



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70-49 



(a) The unit load per outlet as required in other provisions 
of this section 

(b) At 200 volt-amperes per linear foot of show window 

(8) Fixed Multioutlet Assemblies. Fixed multioutlet 
assemblies used in other than dwelling units or the guest 
rooms of hotels or motels shall be computed in accordance 
with (a) or (b). 

(a) Where appliances are unlikely to be used simultaneously, 
each 5 ft (1.52 m) or fraction thereof of each separate 
and continuous length shall be considered as one outlet 
of not less than 180 volt-amperes. 

(b) Where appliances are likely to be used simultaneously, 
each 1 ft (305 mm) or fraction thereof shall be considered 
as an outlet of not less than 180 volt-amperes. 

(9) Receptacle Outlets. Except as covered in (10), re- 
ceptacle outlets shall be computed at not less than 180 volt- 
amperes for each single or for each multiple receptacle on 
one strap. A single piece of equipment consisting of a multi- 
ple receptacle comprised of four or more receptacles shall 
be computed at not less than 90 volt-amperes per receptacle. 

This provision shall not be applicable to the receptacle 
outlets specified in Sections 210-1 1(c)(1) and (2). 

(10) Dwelling Occupancies. In one-family, two-family, 
and multifamily dwellings and in guest rooms of hotels and 
motels, the outlets specified in (a), (b), and (c) are included 
in the general lighting load calculations of Section 220-3(a). 
No additional load calculations shall be required for such 
outlets. 

(a) All general-use receptacle outlets of 20-ampere rating 
or less, including receptacles connected to the circuits 
in Section 210-1 1(c)(3) 

(b) The receptacle outlets specified in Sections 210-52(e) 
and (g) 

(c) The lighting outlets specified in Sections 210-70(a) 
and(b) 

(11) Other Outlets. Other outlets not covered in (1) 
through (10) shall be computed based on 180 volt-amperes 
per outlet. 

(c) Loads for Additions to Existing Installations. 

(1) Dwelling Units. Loads for structural additions to an 
existing dwelling unit or to a previously unwired portion of 
an existing dwelling unit, either of which exceeds 500 ft 2 
(46.5 m 2 ), shall be computed in accordance with (b). Loads 
for new circuits or extended circuits in previously wired 
dwelling units shall be computed in accordance with either 
(a)or(b). 

(2) Other than Dwelling Units. Loads for new circuits 
or extended circuits in other than dwelling units shall be 
computed in accordance with either (a) or (b). 



220-4. Maximum Loads. The total load shall not exceed 
the rating of the branch circuit, and it shall not exceed 
the maximum loads specified in (a) through (c) under the 
conditions specified therein. 

(a) Motor-Operated and Combination Loads. Where a 
circuit supplies only motor-operated loads, Article 430 shall 
apply. Where a circuit supplies only air-conditioning equip- 
ment, refrigerating equipment, or both, Article 440 shall 
apply. For circuits supplying loads consisting of motor-oper- 
ated utilization equipment that is fastened in place and that 
has a motor larger than Va hp in combination with other 
loads, the total computed load shall be based on 125 percent 
of the largest motor load plus the sum of the other loads. 

(b) Inductive Lighting Loads. For circuits supplying 
lighting units that have ballasts, transformers, or autotrans- 
formers, the computed load shall be based on the total ampere 
ratings of such units and not on the total watts of the lamps. 

(c) Range Loads. It shall be acceptable to apply demand 
factors for range loads in accordance with Table 220-19, 
including Note 4. 

B. Feeders and Services 

220-10. General. The computed load of a feeder or service 
shall not be less than the sum of the loads on the branch 
circuits supplied, as determined by Part A of this article, 
after any applicable demand factors permitted by Parts B, 

C, or D have been applied. 

FPN: See Examples Dl(a) through D10 in Appendix D. 
See Section 220-4(b) for the maximum load in amperes 
permitted for lighting units operating at less than 100 percent 
power factor. 

I 220-11. General Lighting. The demand factors specified 
in Table 220- 1 1 shall apply to that portion of the total branch- 
circuit load computed for general illumination. They shall 
not be applied in determining the number of branch circuits 
for general illumination. 

220-12. Show-Window and Track Lighting. 

(a) Show Windows. For show-window lighting, a load of 
not less than 200 volt-amperes shall be included for each 
linear foot (305 mm) of show window, measured horizontally 
along its base. 

I FPN: See Section 220-3(b)(7) for branch circuits supplying 
show windows. 

(b) Track Lighting. For track lighting in other than dwell- 
ing units or guest rooms of hotels or motels, an additional 
load of 150 volt-amperes shall be included for every 2 ft 
(610 mm) of lighting track or fraction thereof. 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-50 



ARTICLE 220 — BRANCH-CIRCUIT, FEEDER, AND SERVICE CALCULATIONS 



Table 220-11. Lighting Load Demand Factors 



Type of Occupancy 


Portion of Lighting Load 

to Which Demand Factor 

Applies (Volt-Amperes) 


Demand 

Factor 

(Percent) 


Dwelling units 


First 3000 or less at 
From 3001 to 120,000 at 
Remainder over 120,000 at 


100 

35 
25 


Hospitals* 


First 50,000 or less at 
Remainder over 50,000 at 


40 
20 


Hotels and motels, 
including apartment 
houses without provision 
for cooking by tenants* 


First 20,000 or less at 
From 20,001 to 100,000 at 
Remainder over 100,000 at 


50 
40 
30 


Warehouses (storage) 


First 12,500 or less at 
Remainder over 12,500 at 


100 
50 


All others 


Total volt-amperes 


100 



*The demand factors of this table shall not apply to the computed load of feeders 
or services supplying areas in hospitals, hotels, and motels where the entire lighting 
is likely to be used at one time, as in operating rooms, ballrooms, or dining rooms. 



220-13. Receptacle Loads — Nond welling Units. In other 
than dwelling units, receptacle loads computed at not more 
than 180 volt-amperes per outlet in accordance with Section 
220-3(b)(9) and fixed multi-outlet assemblies computed in 
accordance with Section 220-3(b)(8) shall be permitted to 
be added to the lighting loads and made subject to the 
demand factors given in Table 220-11, or they shall be 
permitted to be made subject to the demand factors given 
in Table 220-13. 

Table 220-13. Demand Factors for Nondwelling Receptacle 
Loads 



Portion of Receptacle Load 

to Which Demand Factor 

Applies (Volt-Amperes) 



Demand Factor 
(Percent) 



First 10 kVA or less at 
Remainder over 10 kVA at 



100 
50 



220-14. Motors. Motor loads shall be computed in accor- 
dance with Sections 430-24, 430-25, and 430-26. 

220-15. Fixed Electric Space Heating. Fixed electric 
space heating loads shall be computed at 100 percent of the 
total connected load; however, in no case shall a feeder or 
service load current rating be less than the rating of the 
largest branch circuit supplied. 

Exception: Where reduced loading of the conductors results 
from units operating on duty-cycle, intermittently, or from 
all units not operating at one time, the authority having 
jurisdiction may grant permission for feeder conductors to 



have an ampacity less than 100 percent, provided the con- 
ductors have an ampacity for the load so determined. 

220-16. Small Appliance and Laundry Loads — Dwell- 
ing Unit. 

(a) Small Appliance Circuit Load. In each dwelling unit, 
the load shall be computed at 1500 volt-amperes for each 
2-wire small-appliance branch circuit required by Section 
210-1 1(c)(1). Where the load is subdivided through two or 
more feeders, the computed load for each shall include not 
less than 1500 volt-amperes for each 2-wire small-appliance 
branch circuit. These loads shall be permitted to be included 
with the general lighting load and subjected to the demand 
factors provided in Table 220-11. 

Exception: The individual branch circuit permitted by Sec- 
tion 210-52(b)^l), Exception No. 2 shall be permitted to be 
excluded from the calculation required by Section 220-16 

(b) Laundry Circuit Load. A load of not less than 1500 
volt-amperes shall be included for each 2-wire laundry 
branch circuit installed as required by Section 210-1 1(c)(2). 
This load shall be permitted to be included with the general 
lighting load and subjected to the demand factors provided 
in Table 220-11. 

220-17. Appliance Load — Dwelling Unit(s). It shall be 
permissible to apply a demand factor of 75 percent to the 
nameplate rating load of four or more appliances fastened 
in place, other than electric ranges, clothes dryers, space- 
heating equipment, or air-conditioning equipment, that are 
served by the same feeder or service in a one-family, two- 
family, or multifamily dwelling. 

220-18. Electric Clothes Dryers — Dwelling Unit(s). The 

load for household electric clothes dryers in a dwelling 
unit(s) shall be 5000 watts (volt-amperes) or the nameplate 
rating, whichever is larger, for each dryer served. The use 
of the demand factors in Table 220-18 shall be permitted. 
Where two or more single-phase dryers are supplied by a 
3-phase, 4- wire feeder or service, the total load shall be 
computed on the basis of twice the maximum number con- 
nected between any two phases. 

220-19. Electric Ranges and Other Cooking Appli- 
ances — Dwelling Unit(s). The demand load for household 
electric ranges, wall-mounted ovens, counter-mounted cook- 
ing units, and other household cooking appliances indi- 
vidually rated in excess of VA kW shall be permitted to be 
computed in accordance with Table 220-19. Where two or 
more single-phase ranges are supplied by a 3-phase, 4-wire 
feeder or service, the total load shall be computed on the 
basis of twice the maximum number connected between any 
two phases. Kilo volt-amperes (kVA) shall be considered 
equivalent to kilowatts (kW) for loads computed under this 
section. 

FPN: See Example D5(a) in Appendix D. 



1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 220 — BRANCH-CIRCUIT, FEEDER, AND SERVICE CALCULATIONS 



70-51 



Table 220-18. Demand Factors for Household Electric Clothes 
Dryers 



Table 220-19. (Continued) 



Number of 
Dryers 



Demand Factor 
(Percent) 



100 
100 
100 
100 
80 
70 



9 

10 

11-13 

14-19 



65 
60 

55 
50 
45 
40 



20-24 
25-29 
30-34 
35-39 
40 and over 



35 

32.5 

30 

27.5 

25 



Table 220-19. Demand Loads for Household Electric Ranges, 
Wall-Mounted Ovens, Counter-Mounted Cooking Units, and 
Other Household Cooking Appliances over VA kW Rating 
(Column A to be used in all cases except as otherwise permitted 
in Note 3.) 





Maximum 








Demand 


Demand Factor 




(kW) 


(Percent) 




(See Notes) 


(See Note 3) 




Column B 


Column C 




Column A 


(Less than 


OVzkWto 


Number of 


(Not over 12 


3V2kW 


8 3 / 4 kW 


Appliances 


k W Rating) 


Rating) 


Rating) 


1 


8 


80 


80 


2 


11 


75 


65 


3 


14 


70 


55 


4 


17 


66 


50 


5 


20 


62 


45 


6 


21 


59 


43 


7 


22 


56 


40 


8 


23 


53 


36 


9 


24 


51 


35 


10 


25 


49 


34 


11 


26 


47 


32 


12 


27 


45 


32 


13 


28 


43 


32 


14 


29 


41 


32 


15 


30 


40 


32 





Maximum 








Demand 


Demand Factor 




(kW) 


(Percent) 




(See Notes) 


(See Note 3) 




Column B 


Column C 




Column A 


(Less than 


(3 l />kWto 


Number of 


(Not over 12 


3Vz kW 


8 3 / 4 kW 


Appliances 


kW Rating) 


Rating) 


Rating) 


16 


31 


39 


28 


17 


32 


38 


28 


18 


33 


37 


28 


19 


34 


36 


28 


20 


' 35 


35 


28 


21 


36 


34 


26 


.22 


37 


33 


26 


23 


38 


32 


26 


24 


39 


31 


26 


25 


40 


30 


26 


26-30 


15 kW + 1 


30 


24 


31-40 


kW for each 
range 


30 


22 


41-50 


25 kW + 3 / 4 


30 


20 


51-60 


k W for each 
range 


30 


18 


61 and over 




30 


16 



Notes: 

1. Over 12 kW through 27 kW ranges all of same rating. For ranges 
individually rated more than 12 kW but not more than 27 kW, the 
maximum demand in Column A shall be increased 5 percent for each 
additional kilowatt of rating or major fraction thereof by which the 
rating of individual ranges exceeds 12 kW. 

2. Over 8 3 /4 kW through 27 kW ranges of unequal ratings. For ranges 
individually rated more than 8 3 /4 kW and of different ratings, but none 
exceeding 27 kW, an average value of rating shall be computed by adding 
together the ratings of all ranges to obtain the total connected load (using 
12 kW for any range rated less than 12 kW) and dividing by the total 
number of ranges. Then the maximum demand in Column A shall be 
increased 5 percent for each kilowatt or major fraction thereof by which 
this average value exceeds 12 kW. 

3. Over P/4 kW through 8% kW. In lieu of the method provided in 
Column A, it shall be permissible to add the nameplate ratings of all 
household cooking appliances rated more than l 3 /4 kW but not more than 
8 3 /4 kW and multiply the sum by the demand factors specified in Column 
B or C for the given number of appliances. Where the rating of cooking 
appliances falls under both Column B and Column C, the demand 
factors for each column shall be applied to the appliances for that column, 
and the results added together. 

4. Branch-Circuit Load. It shall be permissible to compute the branch- 
circuit load for one range in accordance with Table 220-19. The branch- 
circuit load for one wall-mounted oven or one counter-mounted cooking 
unit shall be the nameplate rating of the appliance. The branch-circuit load 
for a counter-mounted cooking unit and not more than two wall-mounted 
ovens, all supplied from a single branch circuit and located in the 'Same 
room, shall be computed by adding the nameplate rating of the individual 
appliances and treating this total as equivalent to one range. 

5. This table also applies to household cooking appliances rated over 
l 3 /4 kW and used in instructional programs. 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-52 



ARTICLE 220 — BRANCH-CIRCUIT, FEEDER, AND SERVICE CALCULATIONS 



FPN No. 1 : See Table 220-20 for commercial cooking 
equipment. 

FPN No. 2: See the examples in Appendix D. 



220-20. Kitchen Equipment — Other Than Dwelling 
Unit(s). It shall be permissible to compute the load for 
commercial electric cooking equipment, dishwasher booster 
heaters, water heaters, and other kitchen equipment in accor- 
dance with Table 220-20. These demand factors shall be 
applied to all equipment that has either thermostatic con- 
trol or intermittent use as kitchen equipment. They shall 
not apply to space-heating, ventilating, or air-conditioning 
equipment. 

However, in no case shall the feeder or service demand 
be less than the sum of the largest two kitchen equipment 
loads. 

Table 220-20. Demand Factors for Kitchen Equipment — 
Other than Dwelling Unit(s) 



220-21. Noncoincident Loads. Where it is unlikely that 
two or more noncoincident loads will be in use simulta- 
neously, it shall be permissible to use only the largest load(s) 
that will be used at one time, in computing the total load 
of a feeder or service. 

220-22. Feeder or Service Neutral Load. The feeder or 
service neutral load shall be the maximum unbalance of the 
load determined by this article. The maximum unbalanced 
load shall be the maximum net computed load between the 
neutral and any one ungrounded conductor, except that the 
load thus obtained shall be multiplied by 140 percent for 3- 
wire, 2-phase or 5-wire, 2-phase systems. For a feeder or 
service supplying household electric ranges, wall-mounted 
ovens, counter-mounted cooking units, and electric dryers, 
the maximum unbalanced load shall be considered as 70 
percent of the load on the ungrounded conductors, as deter- 
mined in accordance with Table 220-19 for ranges and Table 
220-18 for dryers. For 3-wire dc or single-phase ac; 4- 
wire, 3-phase; 3-wire, 2-phase; or 5-wire, 2-phase systems, 
a further demand factor of 70 percent shall be permitted for 
that portion of the unbalanced load in excess of 200 amperes. 



Number of Units 


Demand Factor 


of Equipment 


(Percent) 


1 


100 


2 


100 


3 


90 


4 


80 


5 


70 


6 and over 


65 



There shall be no reduction of the neutral capacity for that 
portion of the load that consists of nonlinear loads supplied 
from a 4-wire, wye-connected, 3-phase system nor the 
grounded conductor of a 3-wire circuit consisting of two 
phase wires and the neutral of a 4-wire, 3-phase, wye-con- 
nected system. 

FPN No. 1: See Examples Dl(a), Dl(b), D2(b), D4(a), and 
D5(a) in Appendix D. 

FPN No. 2: A 3-phase, 4-wire, wye-connected power sys- 
tem used to supply power to nonlinear loads may necessitate 
that the power system design allow for the possibility of 
high harmonic neutral currents. 



C. Optional Calculations for Computing Feeder and 
Service Loads 

220-30. Optional Calculation — Dwelling Unit. 

(a) Feeder and Service Load. For a dwelling unit having 
the total connected load served by a single 3-wire, 120/ 
240-volt or 208Y/120-volt set of service-entrance or feeder 
conductors with an ampacity of 100 or greater, it shall be 
permissible to compute the feeder and service loads in accor 
dance with this section instead of the method specified in 
Part B of this article. The calculated load shall be the result 
of adding the loads from (b) and (c). Feeder and service- 
entrance conductors whose demand load is determined by 
this optional calculation shall be permitted to have the neutral 
load determined by Section 220-22. 

(b) General Loads. The general calculated load shall be 
not less than 100 percent of the first 10 kVA plus 40 percent 
of the remainder of the following loads: 

(1) 1500 volt-amperes for each 2- wire, 20-ampere small- 
appliance branch circuit and each laundry branch circuit 
specified in Section 220-16 

(2) 3 volt-amperes per square foot (0.093 m 2 ) for general 
lighting and general-use receptacles 

(3) The nameplate rating of all appliances that are fastened 
in place, permanently connected, or located to be on a 
specific circuit, ranges, wall-mounted ovens, counter- 
mounted cooking units, clothes dryers, and water heaters 

(4) The nameplate ampere or kVA rating of all motors and 
of all low-power-factpr loads 



(c) Heating and Air-Conditioning Load. Include 
largest of the following six selections (load in kVA). 



the 



(1) 100 percent of the nameplate rating(s) of the air condi- 
tioning and cooling. 

(2) 100 percent of the nameplate ratings of the heat pump 
compressors and supplemental heating unless the con- 



1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 220 — BRANCH-CIRCUIT, FEEDER, AND SERVICE CALCULATIONS 



70-53 



trailer prevents the compressor and supplemental heat- 
ing from operating at the same time. 

(3) 100 percent of the nameplate ratings of electric thermal 
storage and other heating systems where the usual load 
is expected to be continuous at the full nameplate value. 
Systems qualifying under this selection shall not be 
calculated under any other selection in (c). 

(4) 65 percent of the nameplate rating(s) of the central elec- 
tric space heating, including integral supplemental heat- 
ing in heat pumps where the controller prevents the 
compressor and supplemental heating from operating at 
the same time. 

(5) 65 percent of the nameplate rating(s) of electric space 
heating if less than four separately controlled units. 

(6) 40 percent of the nameplate rating(s) of electric space 
heating if four or more separately controlled units. 

220-31. Optional Calculation for Additional Loads in 
Existing Dwelling Unit. For an existing dwelling unit pres- 
ently being served by an existing 120/240- volt or 208 Y/ 
120- volt, 3-wire service, it shall be permissible to compute 
load calculations as follows: 



Load (kVa) 



Percent of Load 



First 8 kVA of load at 
Remainder of load at 



■100 
40 



Load calculations shall include lighting at 3 volt-amperes/ 
ft 2 (0.093 m 2 ); 1500 volt-amperes for each 2- wire, small- 
appliance branch circuit and each laundry branch circuit as 
specified in Section 220-16; range or wall-mounted oven 
and counter-mounted cooking unit; and other appliances that 
are permanently connected or fastened in place, at nameplate 
rating. 

If air-conditioning equipment or electric space-heating 
equipment is to be installed, the following formula shall be 
applied to determine if the existing service is of sufficient 
size. 



Air-conditioning equipment* 

Central electric space heating* 

Less than four separately controlled 
space-heating units* 

First 8 kVA of all other loads 

Remainder of all other loads 

Other loads shall include the following: 



100% 
100% 

100% 

100% 

40% 



*Use larger connected load of air conditioning and space heating, 
but not both. 



(1) 1500 volt-amperes for each 20-ampere appliance circuit 

(2) Lighting and portable appliances at 3 volt-amperes/ft 2 
(0.093 m 2 ) 

(3) Household range or wall-mounted oven and counter- 
mounted cooking unit 

(4) All other appliances fastened in place, including four 
or more separately controlled space-heating units, at 
nameplate rating 

220-32. Optional Calculation — Multifamily Dwelling: 

(a) Feeder or Service Load. It shall be permissible to com- 
pute the feeder or service load of a multifamily dwelling in 
accordance with Table 220-32 instead of Part B of this article 
where all the following conditions are met. 

(1) No dwelling unit is supplied by more than one feeder. 

(2) Each dwelling unit is equipped with electric cooking 
equipment. 

Exception: When the computed load for multifamily dwell- 
ings without electric cooking in Part B of this article exceeds 
that computed under Part C for the identical load plus 
electric cooking (based on 8 kW per unit), the lesser of the 
two loads shall be permitted to be used. 

(3) Each dwelling unit is equipped with either electric space 
heating or air conditioning or both. Feeders and service- 
entrance conductors whose demand load is determined 
by this optional calculation shall be permitted to have 
the neutral load determined by Section 220-22. 

(b) House Loads. House loads shall be computed in accor- 
dance with Part B of this article and shall be in addition to 
the dwelling unit loads computed in accordance with Table 
220-32. 

(c) Connected Loads. The connected load to which the 
demand factors of Table 220-32 apply shall include the 
following. 

(1) 1500 volt- amperes for each 2- wire, 20-ampere small- 
appliance branch circuit and each laundry branch circuit 
specified in Section 220-16. 

(2) 3 volt-amperes/ft 2 (0.093 m 2 ) for general lighting and 
general-use receptacles. 

(3) The nameplate rating of all appliances that are fastened 
in place, permanently connected or located to be on a 
specific circuit, ranges, wall-mounted ovens, counter- 
mounted cooking units, clothes dryers, water heaters, 
and space heaters. If water heater elements are inter- 
locked so that all elements cannot be used at the same 
time, the maximum possible load shall be considered 
the nameplate load. 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-54 



ARTICLE 220 — BRANCH-CIRCUIT, FEEDER, AND SERVICE CALCULATIONS 



(4) The nameplate ampere or kilovolt-ampere rating of all 
motors and of all low-power-factor loads. 

(5) The larger of the air-conditioning load or the space- 
heating load. 

Table 220-32. Optional Calculations — Demand Factors for 
Three or More Multifamily Dwelling Units 



Number of 
Dwelling Units 



Demand Factor 
(Percent) 



3-5 

6-7 

8-10 

11 

12-13 

14-15 



45 
44 
43 
42 
41 
40 



16-17 

18-20 

21 

22-23 
24-25 
26-27 



39 

38 
37 
36 
35 
34 



28-30 

31 
32-33 
34-36 
37-38 
39-12 



33 
32 
31 
30 
29 
28 



43^15 
46-50 
51-55 
56-61 
62 and over 



27 
26 

25 
24 
23 



220-33. Optional Calculation — Two Dwelling Units. 

Where two dwelling units are supplied by a single feeder 
and the computed load under Part B of this article exceeds 
that for three identical units computed under Section 220- 
32, the lesser of the two loads shall be permitted to be used. 

220-34. Optional Method — Schools. The calculation of 
a feeder or service load for schools shall be permitted in 
accordance with Table 220-34 in lieu of Part B of this article 
where equipped with electric space heating or air condition- 
ing, or both. The connected load to which the demand factors 
of Table 220-34 apply shall include all of the interior and 
exterior lighting, power, water heating, cooking, other loads, 
and the larger of the air-conditioning load or space-heating 
load within the building or structure. 

Feeders and service-entrance conductors whose demand 
load is determined by this optional calculation shall be per- 
mitted to have the neutral load determined by Section 220- 



22. Where the building or structure load is calculated by 
this optional method, feeders within the building or structure 
shall have ampacity as permitted in Part B of this article; 
however, the ampacity of an individual feeder shall not be 
required to be larger than the ampacity for the entire building. 
This section shall not apply to portable classroom build- 
ings. 



Table 220-34. Optional Method — Demand Factors for 
Feeders and Service-Entrance Conductors for Schools 



Connected Load 

(VA/ft 2 ) 



Demand Factor 
(Percent) 



The first 3 VA/ft 2 at 
Plus, 

Over 3 to 20 VA/ft 2 at 
Plus, 

Remainder over 20 VA/ft 2 at 



100 

75 
25 



Note: For SI units, 1 ft 2 = 0.093 m 2 



220-35. Optional Calculations for Determining Existing 
Loads. The calculation of a feeder or service load for ex- 
isting installations shall be permitted to use actual maximum 
demand to determine the existing load under the following 
conditions. 

(1) The maximum demand data is available for a 1-year 
period. 

Exception: If the maximum demand data for a 1 -year period 
is not available, the calculated load shall be permitted to 
be based on the maximum demand (measure of average 
power demand over a 15-minute period) continuously re- 
corded over a minimum 30-day period using a recording 
ammeter or power meter connected to the highest loaded 
phase of the feeder or service, based on the initial loading 
at the start of the recording. The recording shall reflect the 
maximum demand of the feeder or service by being taken 
when the building or space is occupied and shall include 
by measurement or calculation the larger of the heating or 
cooling equipment load, and other loads that may be periodic 
in nature due to seasonal or similar conditions. 

(2) The maximum demand at 125 percent plus the new load 
does not exceed the ampacity of the feeder or rating of 
the service. 

(3) The feeder has overcurrent protection in accordance with 
Section 240-3, and the service has overload protection 
in accordance with Section 230-90. 

220-36. Optional Calculation — New Restaurants. Cal- 
culation of a service load or feeder, where the feeder serves 



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ARTICLE 225 — OUTSIDE BRANCH CIRCUITS AND FEEDERS 



70-55 



the total load, for a new restaurant shall be permitted in 
accordance with Table 220-36 in lieu of Part B of this article. 

The overload protection of the service-entrance con- 
ductors shall be in accordance with Sections 230-90 and 
240-3. 

Feeder conductors shall not be required to be of greater 
ampacity than the service-entrance conductors. 

Service-entrance or feeder conductors whose demand 
load is determined by this optional calculation shall be 
permitted to have the neutral load determined by Section 
220-22. 

Table 220-36. Optional Method — Demand Factors for 
Service-Entrance and Feeder Conductors for New Restaurants 



Table 220-40. Method for Computing Farm Loads for Other 
than Dwelling Unit 





All Electric 


Not All Electric 


Total Connected 


Demand Factor 


Demand Factor 


Load (kVA) 


(Percent) 


(Percent) 


0-250 


80 


100 


251-280 


70 


90 


281-325 


60 


80 


326-375 


50 


70 


376-800 


50 


65 


Over 800 


50 


50 



Note: Add all electrical loads, including both heating and cooling loads, 
to compute the total connected load. Select the one demand factor that 
applies from the table and multiply the total connected load by this single 
demand factor. 



D. Method for Computing Farm Loads 

220-40. Farm Loads — Buildings and Other Loads. 

(a) Dwelling Unit. The feeder or service load of a farm 
dwelling unit shall be computed in accordance with the 
provisions for dwellings in Part B or C of this article. Where 
the dwelling has electric heat and the farm has electric grain- 
drying systems, Part C of this article shall not be used to 
compute the dwelling load. 

(b) Other than Dwelling Unit. For each farm building or 
load supplied by two or more separate branch circuits, the 
load for feeders, service-entrance conductors, and service 
equipment shall be computed in accordance with demand 
factors not less than indicated in Table 220-40. 

FPN: See Section 230-21 for overhead conductors from a 
pole to a building or other structure. 

220-41. Farm Loads — Total. The total load of the farm 
for service-entrance conductors and service equipment shall 
be computed in accordance with the farm dwelling unit load 
and demand factors specified in Table 220-41. Where there 
is equipment in two or more farm equipment buildings or 
for loads having the same function, such loads shall be 



Ampere Load at 
240 Volts Maximum 



Demand Factor 
(Percent) 



Loads expected to operate without diversity, 
but not less than 125 percent full-load 
current of the largest motor and not less 
than the first 60 amperes of load 

Next 60 amperes of all other loads 

Remainder of other load 



100 



50 

25 



computed in accordance with Table 220-40 and shall be 
permitted to be combined as a single load in Table 220-41 
for computing the total load. 

FPN: See Section 230-21 for overhead conductors from a 
pole to a building or other structure. 

Table 220-41. Method for Computing Total Farm Load 



Individual Loads 

Computed in Accordance 

with Table 220-40 



Demand Factor 
(Percent) 



Largest load 
Second largest load 
Third largest load 
Remaining loads 



100 
75 
65 
50 



Note: To this total load, add the load of the farm dwelling unit computed 
in accordance with Part B or C of this article. Where the dwelling has 
electric heat and the farm has electric grain-drying systems, Part C of 
this article shall not be used to compute the dwelling load. 



Article 225 — Outside Branch Circuits and Feeders 

225-1. Scope. This article covers requirements for outside 
branch circuits and feeders run on or between buildings, 
structures, or poles on the premises; and electric equipment 
and wiring for the supply of utilization equipment that is 
located on or attached to the outside of buildings, structures, 
or poles. 

FPN: For additional information on wiring over 600 volts, 
see National Electrical Safety Code, ANSI C2-1997. 



225-2. Other Articles. Application of other articles, in- 
cluding additional requirements to specific cases of equip- 
ment and conductors, is as follows: 



NATIONAL ELECTRICAL CODE 



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70-56 



ARTICLE 225 — OUTSIDE BRANCH CIRCUITS AND FEEDERS 



Article 

Branch circuits 210 

Class 1, Class 2, and Class 3 remote-control, 725 

signaling, and power-limited circuits 

Communications circuits 800 

Community antenna television and radio 820 

distribution systems 

Conductors for general wiring 310 

Electrically driven or controlled irrigation 675 

machines 

Electric signs and outline lighting 600 

Feeders 215 

Fire alarm systems 760 

Fixed outdoor electric deicing and snow-melting 426 

equipment 

Floating buildings 553 

Grounding , 250 

Hazardous (classified) locations 500 

Hazardous (classified) locations — specific 510 

Marinas and boatyards 555 

Messenger supported wiring 321 

Open wiring on insulators 320 

Over 600 volts, general 490 

Overcurrent protection 240 

Radio and television equipment 810 

Services 230 

Solar photovoltaic systems 690 

Swimming pools, fountains, and similar 680 

installations 

Use and identification of grounded conductors 200 



A. General 

225-3. Calculation of Load. 

(a) Branch Circuits. The load on outdoor branch circuits 
shall be as determined by Section 220-3. 

(b) Feeders. The load on outdoor feeders shall be as deter- 
mined by Part B of Article 220. 

225-4. Conductor Covering. Where within 10 ft (3.05 m) 
of any building or structure other than supporting poles or 
towers, open individual (aerial) overhead conductors shall 
be insulated or covered. Conductors in cables or raceways, 
except Type MI cable, shall be of the rubber-covered type 
or thermoplastic type and, in wet locations, shall comply 
with Section 310-8. Conductors for festoon lighting shall 
be of the rubber-covered or thermoplastic type. 

Exception: Equipment grounding conductors and grounded 
circuit conductors shall be permitted to be bare or covered 
as specifically permitted elsewhere in this Code. 



225-5. Size of Conductors. The ampacity of outdoor 
branch-circuit and feeder conductors shall be in accordance 
with Section 310-15 based on loads as determined under 
Section 220-3 and Part B of Article 220. 

225-6. Conductor Size and Support. 

(a) Overhead Spans. Open individual conductors shall not 
be smaller than the following: 

(1) For 600 volts, nominal, or less, No. 10 copper or No. 8 
aluminum for spans up to 50 ft (15.2 m) in length and 
No. 8 copper or No. 6 aluminum for a longer span, 
unless supported by a messenger wire 

(2) For over 600 volts, nominal, No. 6 copper or No. 4 
aluminum where open individual conductors and No. 8 
copper or No. 6 aluminum where in cable 

(b) Festoon Lighting. Overhead conductors for festoon 
lighting shall not be smaller than No. 12 unless the conduc- 
tors are supported by messenger wires. In all spans exceeding 
40 ft (12.2 m), the conductors shall be supported by messen- 
ger wire. The messenger wire shall be supported by strain 
insulators. Conductors or messenger wires shall not be 
attached to any fire escape, down spout, or plumbing equip- 
ment. 

225-7. Lighting Equipment Installed Outdoors. 

(a) General. For the supply of lighting equipment installed 
outdoors, the branch circuits shall comply with Article 210 
and (b) through (d). 

(b) Common Neutral. The ampacity of the neutral con- 
ductor shall not be less than the maximum net computed load 
current between the neutral and all ungrounded conductors 
connected to any one phase of the circuit. 

(c) 277 Volts to Ground. Circuits exceeding 120 volts, 
nominal, between conductors and not exceeding 277 volts, 
nominal, to ground shall be permitted to supply lighting 
fixtures for illumination of outdoor areas of industrial estab- 
lishments, office buildings, schools, stores, and other com- 
mercial or public buildings where the fixtures are not less 
than 3 ft (914 mm) from windows, platforms, fire escapes, 
and the like. 

(d) 600 Volts Between Conductors. Circuits exceeding 
277 volts, nominal, to ground and not exceeding 600 volts, 
nominal, between conductors shall be permitted to supply 
the auxiliary equipment of electric-discharge lamps in accor- 
dance with Section 210-6(d)(l). 

225-9. Overcurrent Protection. Overcurrent protection 
shall be in accordance with Section 210-20 for branch cir- 
cuits and Article 240 for feeders. 



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ARTICLE 225 — OUTSIDE BRANCH CIRCUITS AND FEEDERS 



70-57 



225-10. Wiring on Buildings. The installation of outside 
wiring on surfaces of buildings shall be permitted for circuits 
of not over 600 volts, nominal, as open wiring on insulators, 
as multiconductor cable, as Type MC cable, as Type MI 
cable, as messenger supported wiring, in rigid metal conduit, 
in intermediate metal conduit, in rigid nonmetallic conduit, 
in cable trays, as cablebus, in wireways, in auxiliary gutters, 
in electrical metallic tubing, in flexible metal conduit, in 
liquidtight flexible metal conduit, in liquidtight flexible non- 
metallic conduit, and in busways. Circuits of over 600 volts, 
nominal, shall be installed as provided in Section 300-37. 
Circuits for signs and outline lighting shall be installed in 
accordance with Article 600. 

225-11. Circuit Exits and Entrances. Where outside 
branch and feeder circuits leave or enter a building, the 
requirements of Sections 230-52 and 230-54 shall apply. 

225-12. Open-Conductor Supports. Open conductors 
shall be supported on glass or porcelain knobs, racks, brack- 
ets, or strain insulators. 

225-14. Open-Conductor Spacings. 

(a) 600 Volts, Nominal, or Less. Conductors of 600 volts, 
nominal, or less, shall comply with the spacings provided 
in Table 230-5 1(c). 

(b) Over 600 Volts, Nominal. Conductors of over 600 
volts, nominal, shall comply with the spacings provided in 
Sections 110-36 and 490-24. 

(c) Separation from Other Circuits. Open conductors 
shall be separated from open conductors of other circuits or 
systems by not less than 4 in. (102 mm). 

(d) Conductors on Poles. Conductors on poles shall have 
a separation of not less than 1 ft (305 mm) where not placed 
on racks or brackets. Conductors supported on poles shall pro- 
vide a horizontal climbing space not less than the following: 

(1) Power conductors below communications conduc- 
tors — 30 in. (762 mm) 

(2) Power conductors alone or above communications con- 
ductors: 

300 volts or less — 24 in. (610 mm) 
Over 300 volts — 30 in. (762 mm) 

(3) Communications conductors below power conductors 
— same as power conductors 

(4) Communications conductors alone — no requirement 

225-15. Supports Over Buildings. Supports over a build- 
ing shall be in accordance with Section 230-29. 



225-16. Point of Attachment to Buildings. The point of 
attachment to a building shall be in accordance with Section 
230-26. 

225-17. Means of Attachment to Buildings. The means 
of attachment to a building shall be in accordance with 
Section 230-27. 

225-18. Clearance from Ground. Overhead spans of open 
conductors and open multiconductor cables of not over 600 
volts, nominal, shall conform to the following: 

10 ft (3.05 m) — above finished grade, sidewalks, or 
from any platform or projection from which they might 
I be reached where the voltage does not exceed 150 volts 
to ground and accessible to pedestrians only 

12 ft (3.66 m) — Over residential property and driveways, 

and those commercial areas not subject to truck traffic 

I where the voltage does not exceed 300 volts to ground 

15 ft (4.57 m) — for those areas listed in the 12-ft (3.66- 
m) classification where the voltage exceeds 300 volts to 
ground 

1 8 ft (5.49 m) — over public streets, alleys, roads, parking 
areas subject to truck traffic, driveways on other than 
residential property, and other land traversed by vehicles 
such as cultivated, grazing, forest, and orchard 

FPN: For clearances of conductors of over 600 volts, see 
I National Electrical Safety Code, ANSI C2-1997. 

225-19. Clearances from Buildings for Conductors of 
Not Over 600 Volts, Nominal. 

(a) Above Roofs. Overhead spans of open conductors and 
open multiconductor cables shall have a vertical clearance 
of not less than 8 ft (2.44 m) above the roof surface. The 
.vertical clearance above the roof level shall be maintained 
for a distance not less than 3 ft (914 mm) in all directions 
from the edge of the roof. 

Exception No. 1 : The area above a roof surface subject to 
pedestrian or vehicular traffic shall have a vertical clear- 
ance from the roof surface in accordance with the clearance 
requirements of Section 225-18. 

Exception No. 2: Where the voltage between conductors 
does not exceed 300, and the roof has a slope of 4 in. (102 
I mm) in 12 in. (305 mm) or greater, a reduction in clearance 
to 3 ft (914 mm) shall be permitted. 

Exception No. 3: Where the voltage between conductors 
does not exceed 300, a reduction in clearance above only 
the overhanging portion of the roof to not less than 18 in. 
(457 mm) shall be permitted if (1) not more than 6 ft (1.83 
m) of the conductors, 4 ft (1.22 m) horizontally, pass above 



NATIONAL ELECTRICAL CODE 



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70-58 



ARTICLE 225 — OUTSIDE BRANCH CIRCUITS AND FEEDERS 



the roof overhang, and (2) they are terminated at a through- 
the-roof raceway or approved support. 

Exception No. 4: The requirement for maintaining the ver- 
tical clearance 3 ft (914 mm) from the edge of the roof shall 
not apply to the final conductor span where the conductors 
are attached to the side of a building. 

(b) From Nonbuilding or Nonbridge Structures. From 
signs, chimneys, radio and television antennas, tanks, and 
other nonbuilding or nonbridge structures, clearances — 
vertical, diagonal, and horizontal — shall not be less than 
3 ft (914 mm). 

(c) Horizontal Clearances. Clearances shall not be less 
than 3 ft (914 mm). 

(d) Final Spans. Final spans of feeders or branch circuits 
to a building they supply or from which they are fed shall 
be permitted to be attached to the building, but they shall 
be kept not less than 3 ft (914 mm) from windows that are 
designed to be opened, doors, porches, balconies, ladders, 
stairs, fire escapes, or similar locations. Vertical clearance 
of final spans above, or within 3 ft (914 mm) measured 
horizontally of, platforms, projections, or surfaces from 
which they might be reached shall be maintained in accor- 
dance with Section 225-18. 

Exception: Conductors run above the top level of a window 
shall be permitted to be less than the 3 ft (914 mm) require- 
ment above. 

Overhead branch-circuit and feeder conductors shall not 
be installed beneath openings through which materials may 
be moved, such as openings in farm and commercial build- 
ings, and shall not be installed where they will obstruct 
entrance to these building openings. 

(e) Zone for Fire Ladders. Where buildings exceed three 
stories or 50 ft (15.2 m) in height, overhead lines shall be 
arranged, where practicable, so that a clear space (or zone) 
at least 6 ft (1.83 m) wide will be left either adjacent to the 
buildings or beginning not over 8 ft (2.44 m) from them 
to facilitate the raising of ladders when necessary for fire 
fighting. 

FPN: For clearance of conductors over 600 volts, see Na- 
tional Electrical Safety Code, ANSI C2-1997. 

225-20. Mechanical Protection of Conductors. Mechani- 
cal protection of conductors on buildings, structures, or poles 
shall be as provided for services in Section 230-50. 

225-21. Multiconductor Cables on Exterior Surfaces of 
Buildings. Supports for multiconductor cables on exterior 
surfaces of buildings shall be as provided in Section 
230-51. 



225-22. Raceways on Exterior Surfaces of Build- 
ings. Raceways on exterior surfaces of buildings shall be 
raintight and arranged to drain. 

Exception: Flexible metal conduit, where permitted in Sec- 
tion 350-5(1), shall not be required to be raintight. 

225-24. Outdoor Lampholders. Where outdoor 1am- 
pholders are attached as pendants, the connections to the 
circuit wires shall be staggered. Where such lampholders 
have terminals of a type that puncture the insulation and 
make contact with the conductors, they shall be attached 
only to conductors of the stranded type. 

225-25. Location of Outdoor Lamps. Locations of lamps 
for outdoor lighting shall be below all energized conductors, 
transformers, or other electric utilization equipment, unless 

(1) Clearances or other safeguards are provided, for relamp- 
ing operations, or 

(2) Equipment is controlled by a disconnecting means that 
can be locked in the open position. 

225-26. Vegetation. Vegetation such as trees shall not be 
used for support of overhead conductor spans ; 

Exception: For temporary wiring in accordance with A rticle 
305. 



B. More than One Building or Other Structure 

225-30. Number of Supplies. Where more than one build- 
ing or other structure is on the same property and under 
single management, each building or other structure served 
shall be supplied by one feeder or branch circuit unless 
permitted in (a) through (e). For the purpose of this section, 
a multiwire branch circuit shall be considered a single circuit. 

(a) Special Conditions. Additional feeders or branch cir- 
cuits shall be permitted to supply the following: 

(1) Fire pumps 

(2) Emergency systems 

(3) Legally required standby systems 

(4) Optional standby systems 

(5) Parallel power production systems 

(b) Special Occupancies. By special permission, addi- 
tional feeders or branch circuits shall be permitted for 

(1) Multiple-occupancy buildings where there is no avail- 
able space for supply equipment accessible to all occu- 
pants, or 

(2) A single building or other structure sufficiently large to 
make two or more supplies necessary. 



1999 Edition 



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ARTICLE 225 — OUTSIDE BRANCH CIRCUITS AND FEEDERS 



70-59 



(c) Capacity Requirements. Additional feeders or branch 
circuits shall be permitted where the capacity requirements 
are in excess of 2000 amperes at a supply voltage of 600 
volts or less. 

(d) Different Characteristics. Additional feeders or 
branch circuits shall be permitted for different voltages, 
frequencies, or phases, or for different uses, such as control 
of outside lighting from multiple locations. 

(e) Documented Switching Procedures. Additional feed- 
ers or branch circuits shall be permitted to supply instal- 
lations under single management where documented safe 
switching procedures are established and maintained for dis- 
connection. 

225-31. Disconnecting Means. Means shall be provided 
for disconnecting all ungrounded conductors that supply or 
pass through the building or structure. 

225-32. Location. The disconnecting means shall be in- 
stalled either inside or outside of the building or structure 
served or where the conductors pass through the building 
or structure. The disconnecting means shall be at a readily 
accessible location nearest the point of entrance of the con- 
ductors. For the purposes of this section, the requirements 
in Section 230-6 shall be permitted to be utilized. 

Exception No. 1: For installations under single manage- 
ment, where documented safe switching procedures are 
established and maintained for disconnection, the discon- 
necting means shall be permitted to be located elsewhere 
on the premises. 

Exception No. 2: For buildings or other structures qualify- 
ing under the provisions of Article 685, the disconnecting 
means shall be permitted to be located elsewhere on the 
premises. 

Exception No. 3: For towers or poles used as lighting stan- 
dards, the disconnecting means shall be permitted to be 
located elsewhere on the premises. 

Exception No. 4: For poles or similar structures used only 
for support of signs installed in accordance with Article 
600, the disconnecting means shall be permitted to be located 
elsewhere on the premises. 

225-33. Maximum Number of Disconnects. 

(a) General. The disconnecting means for each supply per- 
mitted by Section 225-30 shall consist of not more than six 
switches or six circuit breakers mounted in a single enclo- 
sure, in a group of separate enclosures, or in or on a switch- 
board. There shall be no more than six disconnects per 
supply grouped in any one location. 

Exception: For the purpose of this section, disconnecting 
means used solely for the control circuit of the ground-fault 



protection system, installed as part of the listed equipment, 
shall not be considered a supply disconnecting means. 

(b) Single-Pole Units. Two or three single-pole switches 
or breakers, capable of individual operation, shall be permit- 
ted on multiwire circuits, one pole for each ungrounded 
conductor, as one multipole disconnect, provided they are 
equipped with handle ties or a master handle to disconnect 
all ungrounded conductors with no more than six operations 
of the hand. 

225-34. Grouping of Disconnects. 

(a) General. The two to six disconnects as permitted in 
Section 225-33 shall be grouped. Each disconnect shall be 
marked to indicate the load served. 

Exception: One of the two to six disconnecting means per- 
mitted in Section 225-33, where used only for a water pump 
also intended to provide fire protection, shall be permitted 
to be located remote from the other disconnecting means. 

(b) Additional Disconnecting Means. The one or more 
additional disconnecting means for fire pumps or for emer- 
gency, legally required standby, or optional standby system 
permitted by Section 225-30 shall be installed sufficiently 
remote from the one to six disconnecting means for normal 
supply to minimize the possibility of simultaneous interrup- 
tion of supply. 

225-35. Access to Occupants. In a multiple-occupancy 
building, each occupant shall have access to the occupant's 
supply disconnecting means. 

Exception: In a multiple-occupancy building where electric 
supply and electrical maintenance are provided by the build- 
ing management and where these are under continuous 
building management supervision, the supply disconnecting 
means supplying more than one occupancy shall be permit- 
ted to be accessible to authorized management personnel 
only. 

225-36. Suitable for Service Equipment. The discon- 
necting means specified in Section 225-31 shall be suitable 
for use as service equipment. 

Exception: For garages and outbuildings on residential 
property, a snap switch or a set of 3-way or 4-way snap 
switches shall be permitted as the disconnecting means. 

225-37. Identification. Where a building or structure has 
any combination of feeders, branch circuits, or services pass- 
ing through it or supplying it, a permanent plaque or directory 
shall be installed at each feeder and branch-circuit disconnect 
location denoting all other services, feeders, or branch cir- 
cuits supplying that building or structure or passing through 



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ARTICLE 225 — OUTSIDE BRANCH CIRCUITS AND FEEDERS 



that building or structure and the area served by each. See 
Section 230-2(e). 

Exception No. 1: A plaque or directory shall not be required 
for large capacity multibuilding industrial installations 
under single management, where it is ensured that discon- 
nection can be accomplished by establishing and main- 
taining safe switching procedures. 

Exception No. 2: This identification shall not be required 
for branch circuits installed from a dwelling unit to a second 
building or structure. 

225-38. Disconnect Construction. 

(a) Manually or Power Operable. The disconnecting 
means shall consist of either (1) a manually operable switch 
or a circuit breaker equipped with a handle or other suitable 
operating means or (2) a power-operable switch or circuit 
breaker, provided the switch or circuit breaker can be opened 
by hand in the event of a power failure. 

(b) Simultaneous Opening of Poles. Each building or 
structure disconnecting means shall simultaneously discon- 
nect all ungrounded supply conductors that it controls from 
the building or structure wiring system. 

(c) Disconnection of Grounded Conductor. Where the 
building or structure disconnecting means does not dis- 
connect the grounded conductor from the grounded conduc- 
tors in the building or structure wiring, other means shall 
be provided for this purpose at the location of disconnecting 
means. A terminal or bus to which all grounded conductors 
can be attached by means of pressure connectors shall be 
permitted for this purpose. 

In a multisection switchboard, disconnects for the 
grounded conductor shall be permitted to be in any section 
of the switchboard, provided any such switchboard section 
is marked. 

(d) Indicating. The building or structure disconnecting 
means shall plainly indicate whether it is in the open or 
closed position. 

225-39. Rating of Disconnect. The feeder or branch-cir- 
cuit disconnecting means shall have a rating of not less than 
the load to be carried, determined in accordance with Article 
220. In no case shall the rating be lower than specified in 
(a), (b), (c), or (d). 

(a) One-Circuit Installation. For installations to supply 
only limited loads of a single branch-circuit, the branch- 
circuit disconnecting means shall have a rating of not less 
than 15 amperes. 

(b) Two-Circuit Installations. For installations consisting 
of not more than two 2-wire branch circuits, the feeder or 



branch-circuit disconnecting means shall have a rating of 
not less than 30 amperes. 

(c) One-Family Dwelling. For a one-family dwelling, the 
feeder disconnecting means shall have a rating of not less 
than 100 amperes, 3-wire. 

(d) All Others. For all other installations, the feeder or 
branch-circuit disconnecting means shall have a rating of 
not less than 60 amperes. 

225-40. Access to Overcurrent Protective Devices. 

Where a feeder overcurrent device is not readily accessible, 
branch-circuit overcurrent devices shall be installed on the 
load side, shall be mounted in a readily accessible location, 
and shall be of a lower ampere rating than the feeder over- 
current device. 



C. Over 600 Volts 

225-50. Warning Signs. Signs with the words "WARN- 
ING — HIGH VOLTAGE — KEEP OUT" shall be posted 
in plain view where unauthorized persons might come in 
contact with live parts. 

225-51. Isolating Switches. Where oil switches or air, oil, 
vacuum, or sulfur hexafluoride circuit breakers constitute a 
building disconnecting means, an isolating switch with visi- 
ble break contacts and meeting the requirements of Section 
230-204(b), (c), and (d) shall be installed on the supply side 
of the disconnecting means and all associated equipment. 

Exception: The isolating switch shall not be required where 
the disconnecting means is mounted on removable truck 
panels or metal-enclosed switchgear units that cannot be 
opened unless the circuit is disconnected and that, when 
removed from the normal operating position, automatically 
disconnect the circuit breaker or switch from all energized 
parts. 

225-52. Location. A building or structure disconnecting 
means shall be located in accordance with Section 225-32, 
or it shall be electrically operated by a similarly located 
remote-control device. 

225-53. Type. Each building or structure disconnect shall 
simultaneously disconnect all ungrounded supply con- 
ductors it controls and shall have a fault-closing rating not 
less than the maximum available short-circuit current avail- 
able at its supply terminals. 

Where fused switches or separately mounted fuses are 
installed, the fuse characteristics shall be permitted to con- 
tribute to the fault closing rating of the disconnecting means. 



1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 230 — SERVICES 



70-61 



Article 230 — Services 

230-1. Scope. This article covers service conductors and 
equipment for control and protection of services and their 
installation requirements. 

FPN: See Figure 230-1. 



General Part A 

Overhead Service-Drop Conductors Part B 

Underground Service-Lateral Conductors Part C 

Service-Entrance Conductors Part D 

Service Equipment— General Part E 

Service Equipment — Disconnecting Means Part F 

Service Equipment — Overcurrent Protection Part G 

Services Exceeding 600 Volts, Nominal Part H 

Source 



Overhead 
Last pole 


t 


k 


Underground 
Street main 


Part B Service drop 
230-24 Clearances 

Service head 




Service lateral Part C 

Depth of burial 230-49 
and protection 

Terminal box, 
meter, or other 
enclosure 


















Service-entrance 
conductors 


PartD 


Service equipment — General 
Grounding 


C 


i , 


PartE 
Article 250 



Disconnecting means 


1 




PartF 


Overcurrent protection 




PartG 










Branch circuits 
Feeders 


Articles 210, 225 
Articles 215, 225 











Figure 230-1 Services. 



A. General 



230-2. Number of Services. A building or other structure 
served shall be supplied by only one service unless permitted 
in (a) through (d). For the purpose of Section 230-40, Excep- 
tion No. 2 only, underground sets of conductors, size 1/0 and 
larger, running to the same location and connected together at 
their supply end, but not connected together at their load 
end, shall be considered to be supplying one service. 

(a) Special Conditions. Additional services shall be per- 
mitted to supply 



(1) Fire pumps 

(2) Emergency systems 

(3) Legally required standby systems 

(4) Optional standby systems 

(5) Parallel power production systems 

(b) Special Occupancies. By special permission, addi- 
tional services shall be permitted for 

(1) Multiple-occupancy buildings where there is no avail- 
able space for service equipment accessible to all occu- 
pants, or 

(2) A single building or other structure sufficiently large to 
make two or more services necessary. 

(c) Capacity Requirements. 

(1) Additional services shall be permitted where the ca- 
pacity requirements are in excess of 2000 amperes at a 
supply voltage of 600 volts or less. 

(2) Additional services shall be permitted where the load 
requirements of a single-phase installation are greater than 
the serving agency normally supplies through one service. 

(3) Additional services shall be permitted by special per- 
mission. 

(d) Different Characteristics. Additional services shall be 
permitted for different voltages, frequencies, or phases, or 
for different uses, such as for different rate schedules. 

(e) Identification. Where a building or structure is supplied 
by more than one service, or any combination of branch 
circuits, feeders, and services, a permanent plaque or direc- 
tory shall be installed at each service disconnect location 
denoting all other services, feeders, and branch circuits sup- 
plying that building or structure and the area served by each. 
See Section 225-37. 

230-3. One Building or Other Structure Not to Be Sup- 
plied Through Another. Service conductors supplying a 
building or other structure shall not pass through the interior 
of another building or other structure. 

230-6. Conductors Considered Outside the Building. 

Conductors shall be considered outside of a building or other 
structure under any of the following conditions: 

(1) Where installed under not less than 2 in. (50.8 mm) of 
concrete beneath a building or other structure 

(2) Where installed within a building or other structure in 
a raceway that is encased in concrete or brick not less 
than 2 in. (50.8 mm) thick 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-62 



ARTICLE 230 — SERVICES 



(3) Where installed in a transformer vault conforming to 
the requirements of Article 450, Part C 

230-7. Other Conductors in Raceway or Cable. Con- 
ductors other than service conductors shall not be installed 
in the same service raceway or service cable. 

Exception No. 1: Grounding conductors and bonding 
jumpers. 

Exception No. 2: Load management control conductors hav- 
ing overcurrent protection. 

230-8. Raceway Seal. Where a service raceway enters a 
building or structure from an underground distribution sys- 
tem, it shall be sealed in accordance with Section 300-5. 
Spare or unused raceways shall also be sealed. Sealants shall 
be identified for use with the cable insulation, shield, or 
other components. 

230-9. Clearance from Building Openings. Service con- 
ductors installed as open conductors or multiconductor cable 
without an overall outer jacket shall have a clearance of not 
less than 3 ft (914 mm) from windows that are designed to 
be opened, doors, porches, balconies, ladders, stairs, fire 
escapes, or similar locations. Vertical clearance of final spans 
above, or within 3 ft (914 mm) measured horizontally of, 
platforms, projections, or surfaces from which they might 
be reached shall be maintained in accordance with Section 
230-24(b). 

Exception: Conductors run above the top level of a window 
shall be permitted to be less than the 3ft (914 mm) require- 
ment above. 

Overhead service conductors shall not be installed be- 
neath openings through which materials may be moved, such 
as openings in farm and commercial buildings, and shall 
not be installed where they will obstruct entrance to these 
building openings. 

B. Overhead Service-Drop Conductors 

230-21. Overhead Supply. Overhead service conductors 
to a building or other structure (such as a pole) on which a 
meter or disconnecting means is installed shall be considered 
as a service drop and installed accordingly. 

I FPN: For example, see farm loads in Part D of Article 220. 

I 230-22. Insulation or Covering. Individual conductors 
shall be insulated or covered with an extruded thermoplastic 
or thermosetting insulating material. 

Exception: The grounded conductor of a multiconductor 
cable shall be permitted to be bare. 



230-23. Size and Rating. 

(a) General. Conductors shall have sufficient ampacity to 
carry the current for the load as computed in accordance with 
Article 220 and shall have adequate mechanical strength. 

(b) Minimum Size. The conductors shall not be smaller 
than No. 8 copper or No. 6 aluminum or copper-clad alumi- 
num. 

Exception: Conductors supplying only limited loads of a 
single branch circuit — such as small polyphase power, con- 
trolled water heaters, and similar loads — shall not be 
smaller than No. 12 hard-drawn copper or equivalent. 

(c) Grounded Conductors. The grounded conductor shall 
not be less than the minimum size as required by Section 
250-24(b). 

230-24. Clearances. The vertical clearances of all service- 
drop conductors shall be based on conductor temperature of 
60°F (15°C), no wind, with final unloaded sag in the wire, 
conductor, or cable. 

Service-drop conductors shall not be readily accessible 
and shall comply with (a) through (d) for services not over 
600 volts, nominal. 

(a) Above Roofs. Conductors shall have a vertical clear- 
ance of not less than 8 ft (2.44 m) above the roof surface. The 
vertical clearance above the roof level shall be maintained for 
a distance of not less than 3 ft (914 mm) in all directions 
from the edge of the roof. 

Exception No. 1: The area above a roof surface subject to 
pedestrian or vehicular traffic shall have a vertical clear- 
ance from the roof surface in accordance with the clearance 
requirements of Section 230-24(b). 

Exception No. 2: Where the voltage between conductors 
does not exceed 300 and the roof has a slope of 4 in. (102 
mm) in 12 in. (305 mm), or greater, a reduction in clearance 
to 3 ft (914 mm) shall be permitted. 

Exception No. 3: Where the voltage between conductors 
does not exceed 300, a reduction in clearance above only 
the overhanging portion of the roof to not less than 18 in. 
(457 mm) shall be permitted if (1) not more than 6 ft (1.83 
m) of service-drop conductors, 4 ft (1.22 m) horizontally, 
pass above the roof overhang, and (2) they are terminated 
at a through-the-roof raceway or approved support. 

FPN: See Section 230-28 for mast supports. 

Exception No. 4: The requirement for maintaining the ver- 
tical clearance 3 ft (914 mm) from the edge of the roof shall 
not apply to the final conductor span where the service drop 
is attached to the side of a building. 



1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 230 — SERVICES 



70-63 



(b) Vertical Clearance from Ground. Service-drop con- 
ductors where not in excess of 600 volts, nominal, shall 
have the following minimum clearance from final grade: 

10 ft (3.05 m) — at the electric service entrance to build- 
ings, also at the lowest point of the drip loop of the 
building electric entrance, and above areas or sidewalks 
accessible only to pedestrians, measured from final grade 
or other accessible surface only for service-drop cables 
supported on and cabled together with a grounded bare 
messenger where the voltage does not exceed 150 volts 
to ground 

12 ft (3.66 m) — over residential property and driveways, 
and those commercial areas not subject to truck traffic 
where the voltage does not exceed 300 volts to ground 

15 ft (4.57 m) — for those areas listed in the 12-ft 
(3.66-m) classification where the voltage exceeds 300 
volts to ground 

18 ft (5.49 m) — over public streets, alleys, roads, parking 
areas subject to truck traffic, driveways on other than 
residential property, and other land such as cultivated, 
grazing, forest, and orchard 

(c) Clearance from Building Openings. See Section 
230-9. 

(d) Clearance from Swimming Pools. See Section 680-8. 

230-26. Point of Attachment. The point of attachment of 
the service-drop conductors to a building or other structure 
shall provide the minimum clearances as specified in Section 
230-24. In no case shallthis point of attachment be less than 
10 ft (3.05 m) above finished grade. 

230-27. Means of Attachment. Multiconductor cables 
used for service drops shall be attached to buildings or 
other structures by fittings identified for use with service 
conductors. Open conductors shall be attached to fittings 
identified for use with service conductors or to noncombusti- 
ble, nonabsorbent insulators securely attached to the building 
or other structure. 

230-28. Service Masts as Supports. Where a service mast 
is used for the support of service-drop conductors, it shall 
be of adequate strength or be supported by braces or guys 
to withstand safely the strain imposed by the service drop. 
Where raceway-type service masts are used, all raceway 
fittings shall be identified for use with service masts. Only 
power service-drop conductors shall be permitted to be 
attached to a service mast. 



230-29. Supports Over Buildings. Service-drop conduc- 
tors passing over a roof shall be securely supported by sub- 
stantial structures. Where practicable, such supports shall 
be independent of the building. 



C. Underground Service-Lateral Conductors 

230-30. Insulation. Service-lateral conductors shall be in- 
sulated for the applied voltage. 

Exception: A grounded conductor shall be permitted to be 
uninsulated as follows: 

(a) Bare copper used in a raceway 

(b) Bare copper for direct burial where bare copper is 
judged to be suitable for the soil conditions 

(c) Bare copper for direct burial without regard to soil 
conditions where part of a cable assembly identified for 
underground use 

(d) Aluminum or copper-clad aluminum without individual 
insulation or covering where part of a cable assembly 
identified for underground use in a raceway or for direct 
burial 

230-31. Size and Rating. 

(a) General. Service-lateral conductors shall have suf- 
ficient ampacity to carry the current for the load as computed 
in accordance with Article 220 and shall have adequate 
mechanical strength. 

(b) Minimum Size. The conductors shall not be smaller 
than No. 8 copper or No. 6 aluminum or copper-clad alumi- 
num. 

Exception: Conductors supplying only limited loads of a 
single branch circuit — such as small polyphase power, 
controlled water heaters, and similar loads — shall not be 
smaller than No. 12 copper or No. 10 aluminum or copper- 
clad aluminum. 

(c) Grounded Conductors. The grounded conductor shall 
not be less than the minimum size required by Section 250- 
24(b). 

FPN: Reasonable efficiency of operation can be provided 
when voltage drop is taken into consideration in sizing the 
service-lateral conductors. 

230-32. Protection Against Damage. Underground ser- 
vice-lateral conductors shall be protected against damage in 
accordance with Section 300-5. Service-lateral conductors 
entering a building shall be installed in accordance with 
Section 230-6 or protected by a raceway wiring method 
identified in Section 230-43. 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-64 



ARTICLE 230 — SERVICES 



D. Service-Entrance Conductors 

230-40. Number of Service-Entrance Conductor Sets. 
Each service drop or lateral shall supply only one set of 
service-entrance conductors. 

Exception No. 1: Buildings with one or more than one occu- 
pancy shall be permitted to have one set of service-entrance 
conductors for each class of service run to each occupancy 
or group of occupancies. 

Exception No. 2: Where two to six service disconnecting 
means in separate enclosures are grouped at one location 
and supply separate loads from one service drop or lateral, 
one set of service-entrance conductors, shall be permitted to 
supply each or several such service equipment enclosures. 

Exception No. 3: A single-family dwelling unit and a sepa- 
rate structure shall be permitted to have one set of service- 
entrance conductors run to each from a single service drop 
or lateral. 

Exception No. 4: A two-family dwelling or a multifamily 
dwelling shall be permitted to have one set of service- 
entrance conductors installed to supply the circuits covered 
in Section 210-25. 

Exception No. 5: One set of service-entrance conductors . 
connected to the supply side of the normal service discon- 
necting means shall be permitted to supply each or several 
systems covered by Section 230-82(3). 

230-41. Insulation of Service-Entrance Conductors. 

Service-entrance conductors entering or on the exterior of 
buildings or other structures shall be insulated. 

Exception: A grounded conductor shall be permitted to be 
uninsulated as follows: 

(a) Bare copper used in a raceway or part of a service 
cable assembly 

(b) Bare copper for direct burial where bare copper is 
judged to be suitable for the soil conditions 

(c) Bare copper for direct burial without regard to soil 
conditions where part of a cable assembly identified for 
underground use 

(d) Aluminum or copper-clad aluminum without individual 
insulation or covering where part of a cable assembly 
or identified for underground use in a raceway, or for 
direct burial 

230-42. Minimum Size and Rating. 

(a) General. The ampacity of the service-entrance con- 
ductors before the application of any adjustment or correc- 
tion factors shall not be less than either (1) or (2). Loads 
shall be determined in accordance with Article 220. Ampac- 
ity shall be determined from Section 310-15. The maximum 



allowable current of busways shall be that value for which 
the busway has been listed or labeled. 

(1) The sum of the noncontinuous loads plus 125 percent 
of continuous loads 

(2) The sum of noncontinuous load plus the continuous 
load if the service-entrance conductors terminate in an 
overcurrent device where both the overcurrent device 
and its assembly are listed for operation at 100 percent 
of their rating 

(b) Ungrounded Conductors. Ungrounded conductors 
shall have an ampacity of not less than the minimum rating 
of the disconnecting means specified in Section 230-79. 

(c) Grounded Conductors. The grounded conductor shall 
not be less than the minimum size, as required by Section 
250-24(b). 

230-43. Wiring Methods for 600 Volts, Nominal, or Less. 

Service-entrance conductors shall be installed in accordance 
with the applicable requirements of this Code covering the 
type of wiring method used and shall be limited to the 
following methods: 

(1) Open wiring on insulators 

(2) Type IGS cable 

(3) Rigid metal conduit 

(4) Intermediate metal conduit 

(5) Electrical metallic tubing 

(6) Electrical nonmetallic tubing (ENT) 

(7) Service-entrance cables 

(8) Wireways 

(9) Busways 

(10) Auxiliary gutters 

(11) Rigid nonmetallic conduit 

(12) Cablebus 

(13) Type MC cable 

(14) Mineral-insulated, metal- sheathed cable 

(15) Flexible metal conduit not over 6 ft (1.83 m) long or 
liquidtight flexible metal conduit not over 6 ft (1.83 
m) long between raceways, or between raceway and 
service equipment, with equipment bonding jumper 
routed with the flexible metal conduit or the liquidtight 
flexible metal conduit according to the provisions of 
Section 250- 102(a), (b), (c), and (e) 

(16) Liquidtight flexible nonmetallic conduit 

Cable tray systems shall be permitted to support cables 
for use as service-entrance conductors in accordance with 
Article 318. 

230-46. Spliced Conductors. Service-entrance conductors 
shall be permitted to be spliced or tapped by clamped or 



1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 230 — SERVICES 



70-65 



bolted connections. Splices shall be made in enclosures or, 
if directly buried, with a listed underground splice kit. 
Splices of conductors shall be made in accordance with 
Sections 110-14, 300-5(e), 300-13, and 300-15. 

230-49. Protection Against Physical Damage — Under- 
ground. Underground service-entrance conductors shall be 
protected against physical damage in accordance with Sec- 
tion 300-5. 

230-50. Protection of Open Conductors and Cables 
Against Damage — Above Ground. Service-entrance con- 
ductors installed above ground shall be protected against 
physical damage as specified in (a) or (b). 

(a) Service Cables. Service cables, where subject to physi- 
cal damage, shall be protected by any of the following: 

(1) Rigid metal conduit 

(2) Intermediate metal conduit 

(3) Rigid nonmetallic conduit suitable for the location 

(4) Electrical metallic tubing 

(5) Other approved means 

(b) Other than Service Cable. Individual open conductors 
and cables other than service cables shall not be installed 
within 10 ft (3.05 m) of grade level or where exposed to 
physical damage. 

Exception: Type MI and Type MC cable shall be permitted 
within 10 ft (3.05 m) of grade level where not exposed to 
physical damage or where protected in accordance with 
Section 300-5(d). 

230-51. Mounting Supports. Cables or individual open 
service conductors shall be supported as specified in (a), 
(b), or (c). 

(a) Service Cables. Service cables shall be supported by 
straps or other approved means within 12 in. (305 mm) of 
every service head, gooseneck, or connection to a raceway 
or enclosure and at intervals not exceeding 30 in. (762 mm). 

(b) Other Cables. Cables that are not approved for mount- 
ing in contact with a building or other structure shall be 
mounted on insulating supports installed at intervals not 
exceeding 15 ft (4.57 m) and in a manner that will maintain 
a clearance of not less than 2 in. (50.8 mm) from the surface 
over which they pass. 

(c) Individual Open Conductors. Individual open con- 
ductors shall be installed in accordance with Table 230- 
51(c). Where exposed to the weather, the conductors shall 
be mounted on insulators or on insulating supports attached 
to racks, brackets, or other approved means. Where not 



exposed to the weather, the conductors shall be mounted on 
glass or porcelain knobs. 

Table 230-51(c). Supports and Clearances for Individual Open 
Service Conductors 





Maximum 


Minimum Clearance 




Distance 


(in.) 






Between 






Maximum 


Supports 


Between 


From 


Volts 


(ft) 


Conductors 


Surface 


600 


9 


6 


2 


600 


15 


12 


2 


300 


■ AVi 


3 


2 


600* 


4 i/ 2 * 


2'/2* 


1* 



Note: For SI units, 1 in. = 25.4 mm; 1 ft = 0.3048 m. 
*Where not exposed to weather. 



230-52. Individual Conductors Entering Buildings or 
Other Structures. Where individual open conductors enter 
a building or other structure, they shall enter through roof 
bushings or through the wall in an upward slant through 
individual, noncombustible, nonabsorbent insulating tubes. 
Drip loops shall be formed on the conductors before they 
enter the tubes. 

230-53. Raceways to Drain. Where exposed to the 
weather, raceways enclosing service-entrance conductors 
shall be raintight and arranged to drain. Where embedded 
in masonry, raceways shall be arranged to drain. 

Exception: As permitted in Section 350-5. 

230-54. Overhead Service Locations. 

(a) Raintight Service Head. Service raceways shall be 
equipped with a raintight service head at the point of connec- 
tion to service-drop conductors. 

(b) Service Cable Equipped with Raintight Service Head 
or Gooseneck. Service cables shall be equipped with a 
raintight service head. 

Exception: Type' SE cable shall be permitted to be formed 
into a gooseneck and taped with a self-sealing weather- 
resistant thermoplastic. 

(c) Service Heads Above Service-Drop Attachment. Ser- 
vice heads and goosenecks in service-entrance cables shall 
be located above the point of attachment of the service-drop 
conductors to the building or other structure. 

Exception: Where it is impracticable to locate the service 
head above the point of attachment, the service head location 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-66 



ARTICLE 230 — SERVICES 



shall be permitted not farther than 24 in. (610 mm) from 
the point of attachment. 

(d) Secured. Service cables shall be held securely in place. 

(e) Separately Bushed Openings. Service heads shall 
have conductors of different potential brought out through 
separately bushed openings. 

Exception: For jacketed multiconductor service cable with- 
out splice. 

(f) Drip Loops. Drip loops shall be formed on individual 
conductors. To prevent the entrance of moisture, service- 
entrance conductors shall be connected to the service-drop 
conductors either (1) below the level of the service head or 
(2) below the level of the termination of the service-entrance 
cable sheath. 

(g) Arranged that Water Will Not Enter Service Race- 
way or Equipment. Service-drop conductors and service- 
entrance conductors shall be arranged so that water will not 
enter service raceway or equipment. 

230-56. Service Conductor with the Higher Voltage to 
Ground. On a 4-wire, delta-connected service where the 
midpoint of one phase winding is grounded, the service 
conductor having the higher phase voltage to ground shall 
be durably and permanently marked by an outer finish that 
is orange in color, or by other effective means, at each 
termination or junction point. 



E. Service Equipment — General 

230-62. Service Equipment — Enclosed or Guarded. 

Energized parts of service equipment shall be enclosed as 
specified in (a), or guarded as specified in (b). 

(a) Enclosed. Energized parts shall be enclosed so that they 
will not be exposed to accidental contact or shall be guarded 
as in (b). 

(b) Guarded. Energized parts that are not enclosed shall 
be installed on a switchboard, panelboard, or control board 
and guarded in accordance with Sections 1 10-18 and 110-27. 
Where energized parts are guarded as provided in Sections 
110-27(a)(l) and (a)(2), a means for locking or sealing 
doors providing access to energized parts shall be provided. 

230-66. Marking. Service equipment rated at 600 volts or 
less shall be marked to identify it as being suitable for use 
as service equipment. Individual meter socket enclosures 
shall not be considered service equipment. 



F. Service Equipment — Disconnecting Means 

230-70. General. Means shall be provided to disconnect 
all conductors in a building or other structure from the 
service-entrance conductors. 

(a) Location. The service disconnecting means shall be 
installed at a readily accessible location either outside of a 
building or structure or inside nearest the point of entrance 
of the service conductors. 

Service disconnecting means shall not be installed in 
bathrooms. 

(b) Marking. Each service disconnect shall be perma- 
nently marked to identify it as a service disconnect. 

(c) Suitable for Use. Each service disconnecting means 
shall be suitable for the prevailing conditions. Service equip- 
ment installed in hazardous (classified) locations shall com- 
ply with the requirements of Articles 500 through 517. 

230-71. Maximum Number of Disconnects. 

(a) General. The service disconnecting means for each ser- 
vice permitted by Section 230-2, or for each set of service- 
entrance conductors permitted by Section 230-40, Exception 
Nos. 1 or 3, shall consist of not more than six switches or 
six circuit breakers mounted in a single enclosure, in a group 
of separate enclosures, or in or on a switchboard. There shall 
be no more than six disconnects per service grouped in any 
one location. For the purpose of this section, disconnecting 
means used solely for power monitoring equipment or the 
control circuit of the ground-fault protection system, in- 
stalled as part of the listed equipment, shall not be considered 
a service disconnecting means. 

(b) Single-Pole Units. Two or three single-pole switches 
or breakers, capable of individual operation, shall be permit- 
ted on multiwire circuits, one pole for each ungrounded 
conductor, as one multipole disconnect, provided they are 
equipped with handle ties or a master handle to disconnect 
all conductors of the service with no more than six operations 
of the hand. 

FPN: See Section 384- 16(a) for service equipment in panel- 
boards, and see Section 430-95 for service equipment in 
motor control centers. 

230-72. Grouping of Disconnects. 

(a) General. The two to six disconnects as permitted in 
Section 230-71 shall be grouped. Each disconnect shall be 
marked to indicate the load served. 

Exception: One of the two to six service disconnecting 
means permitted in Section 230-71, where used only for a 
water pump also intended to provide fire protection, shall be 



• 



1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 230 — SERVICES 



70-67 



permitted to be located remote from the other disconnecting 
means. 

(b) Additional Service Disconnecting Means. The one or 

more additional service disconnecting means for fire pumps, 
for legally required standby, or for optional standby services 
permitted by Section '230-2 shall be installed sufficiently 
remote from the one to six service disconnecting means for 
normal service to minimize the possibility of simultaneous 
interruption of supply. 

(c) Access to Occupants. In a multiple-occupancy build- 
ing, each occupant shall have access to the occupant's service 
disconnecting means. 

Exception: In a multiple-occupancy building where electric 
service and electrical maintenance are provided by the build- 
ing management and where these are under continuous 
building management supervision, the service disconnecting 
means supplying more than one occupancy shall be permit- 
ted to be accessible to authorized management personnel 
only. 

230-74. Simultaneous Opening of Poles. Each service 
disconnect shall simultaneously disconnect all ungrounded 
service conductors that it controls from the premises wiring 
system. 

230-75. Disconnection of Grounded Conductor. Where 
the service disconnecting means does not disconnect the 
grounded conductor from the premises wiring, other means 
shall be provided for this purpose in the service equipment. 
A terminal or bus to which all grounded conductors can be 
attached by means of pressure connectors shall be permitted 
for this purpose. 

In a multisection switchboard, disconnects for the 
grounded conductor shall be permitted to be in any section 
of the switchboard, provided any such switchboard section 
is marked. 

230-76. Manually or Power Operable. The service dis- 
connecting means for ungrounded service conductors shall 
consist of either (1) a manually operable switch or circuit 
breaker equipped with a handle or other suitable operating 
means or (2) a power-operated switch or circuit breaker 
provided the switch or circuit breaker can be opened by 
hand in the event of a power supply failure. 

230-77. Indicating. The service disconnecting means shall 
plainly indicate whether it is in the open or closed position. 



230-79. Rating of Service Disconnecting Means. The ser- 
vice disconnecting means shall have a rating not less than 
the load to be carried, determined in accordance with Article 



220. In no case shall the rating be lower than specified in 
(a), (b), (c), or (d); 

(a) One-Circuit Installation. For installations to supply 
only limited loads of a single branch circuit, the service 
disconnecting means shall have a rating of not less than 15 
amperes. 

(b) Two-Circuit Installations. For installations consisting 
of not more than two 2- wire branch circuits, the service 
disconnecting means shall have a rating of not less than 30 
amperes. 

(c) One-Family Dwelling. For a one-family dwelling, the 
service disconnecting means shall have a rating of not less 
than 100 amperes, 3-wire. 

(d) All Others. For all other installations, the service dis- 
connecting means shall have a rating of not less than 60 
amperes. 

230-80. Combined Rating of Disconnects. Where the ser- 
vice disconnecting means consists of more than one switch 
or circuit breaker, as permitted by Section 230-71, the com- 
bined ratings of all the switches or circuit breakers used 
shall not be less than the rating required by Section 230-79. 

230-81. Connection to Terminals. The service conductors 
shall be connected to the service disconnecting means by 
pressure connectors, clamps, or other approved means. Con- 
nections that depend on solder shall not be used. 

230-82. Equipment Connected to the Supply Side of Ser- 
vice Disconnect. Only the following equipment shall be 
permitted to be connected to the supply side of the service 
disconnecting means: 



(1) Cable limiters or other current- limiting devices 

(2) Meters nominally rated not in excess of 600 volts, pro- 
vided all metal housings and service enclosures are 
grounded in accordance with Article 250 

(3) Instrument transformers (current and voltage), high- 
impedance shunts, surge-protective devices identified 
for use on the supply side of the service disconnect, 
load management devices, and surge arresters 

(4) Taps used only to supply load management devices, 
circuits for stand-by power systems, fire pump equip- 
ment, and fire and sprinkler alarms, if provided with 
service equipment and installed in accordance with 
requirements for service-entrance conductors 

(5) Solar photovoltaic systems or interconnected electric 
power production sources (See Articles 690 or 705 as 
applicable.) 



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1999 Edition 



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ARTICLE 230 — SERVICES 



(6) Control circuits for power-operable service discon- 
necting means, if suitable overcurrent protection and 
disconnecting means are provided 

(7) Ground-fault protection systems where installed as part 
of listed equipment, if suitable overcurrent protection 
and disconnecting means are provided 

G. Service Equipment — Overcurrent Protection 

230-90. Where Required. Each ungrounded service con- 
ductor shall have overload protection. 

(a) Ungrounded Conductor. Such protection shall be pro- 
vided by an overcurrent device in series with each un- 
grounded service conductor that has a rating or setting not 
higher than the allowable ampacity of the conductor. 

Exception No. 1: For motor-starting currents, ratings that 
conform with Sections 430-52, 430-62, and 430-63 shall be 
permitted. 

Exception No. 2: Fuses and circuit breakers with a rating 
or setting that conform with Section 240-3(b) or (c) and 
Section 240-6 shall be permitted. 

Exception No. 3: Two to six circuit breakers or sets of fuses 
shall be permitted as the overcurrent device to provide the 
overload protection. The sum of the ratings of the circuit 
breakers or fuses shall be permitted to exceed the ampacity 
of the service conductors, provided the calculated load in 
accordance with Article 220 does not exceed the ampacity 
of the service conductors. 

Exception No. 4: Overload protection for fire pump supply 
conductors shall conform with Section 695-4(b)(l). 

Exception No. 5: Overload protection for 120/240-volt, 3- 
wire, single-phase dwelling services shall be permitted in 
accordance with the requirements of Section 310-15(b)(6). 

FPN: See Standard for the Installation of Centrifugal Fire 
Pumps, NFPA 20-1996. 

A set of fuses shall be considered all the fuses required 
to protect all the ungrounded conductors of a circuit. Single- 
pole circuit breakers, grouped in accordance with Section 
230-7 1(b), shall be considered as one protective device. 

(b) Not in Grounded Conductor. No overcurrent device 
shall be inserted in a grounded service conductor except a 
circuit breaker that simultaneously opens all conductors of 
the circuit. 

230-91. Location. The service overcurrent device shall be 
an integral part of the service disconnecting means or shall 
be located immediately adjacent thereto. 

230-92. Locked Service Overcurrent Devices. Where the 
service overcurrent devices are locked or sealed, or not 



readily accessible to the occupant,, branch-circuit overcurrent 
devices shall be installed on the load side, shall be mounted 
in a readily accessible location, and shall be of lower ampere 
rating than the service overcurrent device. 

230-93. Protection of Specific Circuits. Where necessary 
to prevent tampering, an automatic overcurrent device that 
protects service conductors supplying only a specific load, 
such as a water heater, shall be permitted to be locked or 
sealed where located so as to be accessible. 

230-94. Relative Location of Overcurrent Device and 
Other Service Equipment. The overcurrent device shall 
protect all circuits and devices. 

Exception No. 1: The service switch shall be permitted on 
the supply side. 

Exception No. 2: High-impedance shunt circuits, surge ar- 
resters, surge-protective capacitors, and instrument trans- 
formers (current and voltage) shall be permitted to be 
connected and installed on the supply side of the service 
disconnecting means as permitted in Section 230-82. 

Exception No. 3: Circuits for load management devices 
shall be permitted to be connected on the supply side of the 
service overcurrent device where separately provided with 
overcurrent protection. 

Exception No. 4: Circuits used only for the operation of fire 
alarm, other protective signaling systems, or the supply to 
fire pump equipment shall be permitted to be connected 
on the supply side of the service overcurrent device where 
separately provided with overcurrent protection. 

Exception No. 5: Meters nominally rated not in excess of 
600 volts, provided all metal housings and service enclosures 
are grounded in accordance with Article 250. 

Exception No. 6: Where service equipment is power opera- 
ble, the control circuit shall be permitted to be connected 
ahead of the service equipment if suitable overcurrent pro- 
tection and disconnecting means are provided. 

230-95. Ground-Fault Protection of Equipment. 

Ground-fault protection of equipment shall be provided for 
solidly grounded wye electrical services of more than 150 
volts to ground, but not exceeding 600 volts phase-to-phase 
for each service disconnect rated 1000 amperes or more. 

The rating of the service disconnect shall be considered 
to be the rating of the largest fuse that can be installed or 
the highest continuous current trip setting for which the 
actual overcurrent device installed in a circuit breaker is 
rated or can be adjusted. 

Definition. Solidly grounded means that the grounded 
I conductor is grounded without inserting any resistor or im- 
pedance device. 



1999 Edition 



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ARTICLE 230 — SERVICES 



70-69 



Exception No. 1: The ground-fault protection provisions of 
this section shall not apply to a service disconnect for a 
continuous industrial process where a nonorderly shutdown 
will introduce additional or increased hazards. 

Exception No. 2: The ground-fault protection provisions of 
this section shall not apply to fire pumps. 

(a) Setting. The ground-fault protection system shall oper- 
ate to cause the service disconnect to open all ungrounded 
conductors of the faulted circuit. The maximum setting of 
the ground-fault protection shall be 1200 amperes, and the 
maximum time delay shall be one second for ground-fault 
currents equal to or greater than 3000 amperes. 

(b) Fuses. If a switch and fuse combination is used, the 
fuses employed shall be capable of interrupting any current 
higher than the interrupting capacity of the switch during a 
time when the ground-fault protective system will not cause 
the switch to open. 

(c) Performance Testing. The ground-fault protection sys- 
tem shall be performance tested when first installed on site. 
The test shall be conducted in accordance with instructions 
that shall be provided with the equipment: A written record 
of this test shall be made and shall be available to the 
authority having jurisdiction. 

FPN No. 1 : Ground-fault protection that functions to open 
the service disconnect will afford no protection from faults 
on the line side of the protective element. It serves only to 
limit damage to conductors and equipment on the load side 
in the event of an arcing ground fault on the load side of 
the protective element. 

FPN No. 2: This added protective equipment at the service 
equipment may make it necessary to review the overall 
wiring system for proper selective overcurrent protection 
coordination. Additional installations of ground-fault protec- 
tive equipment may be needed on feeders and branch circuits 
where maximum continuity of electrical service is necessary. 

FPN No. 3: Where ground-fault protection is provided for 
the service disconnect and interconnection is made with 
another supply system by a transfer device, means or devices • 
may be needed to ensure proper ground-fault sensing by the 
ground-fault protection equipment. 



H. Services Exceeding 600 Volts, Nominal 

230-200. General. Service conductors and equipment used 
on circuits exceeding 600 volts, nominal, shall comply with 
all the applicable provisions of the preceding sections of this 
article and with the following sections, which supplement or 
modify the preceding sections. In no case shall the provisions 
of Part H apply to equipment on the supply side of the 
service point. 

FPN: For clearances of conductors of over 600 volts, nom- 
inal, see National Electrical Safety Code, ANSI C2-1997. 



230-202. Service-Entrance Conductors. Service- 
entrance conductors to buildings or enclosures shall be in- 
stalled to conform to the following. 

(a) Conductor Size. Service-entrance conductors shall not 
be smaller than No. 6 unless in multiconductor cable. Multi- 
conductor cable shall not be smaller than No. 8. 

(b) Wiring Methods. Service-entrance conductors shall be 
installed by one of the wiring methods covered in Sections 
300-37 and 300-50. 

230-203. Warning Signs. Signs with the words "DAN- 
GER — HIGH VOLTAGE — KEEP OUT" shall be posted 
in plain view where unauthorized persons might come in 
contact with energized parts. 

230-204. Isolating Switches. 

(a) Where Required. Where oil switches or air, oil, vac- 
uum, or sulfur hexafluoride circuit breakers constitute the 
service disconnecting means, an isolating switch with visible 
break contacts shall be installed on the supply side of the 
disconnecting means and all associated service equipment. 

Exception: An isolating switch shall not be required where 
the circuit breaker or switch is mounted on removable truck 
panels or metal-enclosed switchgear units, that 

(a) Cannot be opened unless the circuit is disconnected, 
and 

(b) Where all energized parts are automatically discon- 
nected when the circuit breaker or switch is removed 
from the normal operating position. 

(b) Fuses as Isolating Switch. Where fuses are of the type 
that can be operated as a disconnecting switch, a set of such 
fuses shall be permitted as the isolating switch. 

(c) Accessible to Qualified Persons Only. The isolating 
switch shall be accessible to qualified persons only. 

(d) Grounding Connection. Isolating switches shall be 
provided with a means for readily connecting the load side 
conductors to ground when disconnected from the source 
of supply. 

A means for grounding the load side conductors shall 
not be required for any duplicate isolating switch installed 
and maintained by the electric supply company. 

230-205. Disconnecting Means. 

(a) Location. The service disconnecting means shall be 
located in accordance with Section 230-70. 

(b) Type. Each service disconnect shall simultaneously dis- 
connect all ungrounded service conductors that it controls 
and shall have a fault-closing rating that is not less than 



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1999 Edition 



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ARTICLE 240 — OVERCURRENT PROTECTION 



the maximum short-circuit current available at its supply 
terminals. 

Where fused switches or separately mounted fuses are 
installed, the fuse characteristics shall be permitted to con- 
tribute to the fault-closing rating of the disconnecting means. 

(c) Remote Control. For multibuilding, industrial installa- 
tions under single management, the service disconnecting 
means shall be permitted to be located at a separate building 
or structure. In such cases, the service disconnecting means 
shall be permitted to be electrically operated by a readily 
accessible, remote-control device. 

230-206. Overcurrent Devices as Disconnecting Means. 

Where the circuit breaker or alternative for it, as specified 
in Section 230-208 for service overcurrent devices, meets 
the requirements specified in Section 230-205, they shall 
constitute the service disconnecting means. 

230-208. Protection Requirements. A short-circuit pro- 
tective device shall be provided on the load side of, or as 
an integral part of, the service disconnect, and shall protect 
all ungrounded conductors that it supplies. The protective 
device shall be capable of detecting and interrupting all 
values of current, in excess of its trip setting or melting 
point, that can occur at its location. A fuse rated in continuous 
amperes not to exceed three times the ampacity of the con- 
ductor, or a circuit breaker with a trip setting of not more 
than six times the ampacity of the conductors, shall be con- 
sidered as providing the required short-circuit protection. 

FPN: See Tables 310-67 through 310-86 for ampacities of 
conductors rated 2001 volts and above. 

Overcurrent devices shall conform to the following: 

(a) Equipment Type. Equipment used to protect service- 
entrance conductors shall meet the requirements of Article 
490, Part B. 

(b) Enclosed Overcurrent Devices. The restriction to 80 
percent of the rating for an enclosed overcurrent device 
on continuous loads shall not apply to overcurrent devices 
installed in services operating at over 600 volts. 

230-209. Surge Arresters (Lightning Arresters). Surge 
arresters installed in accordance with the requirements of 
Article 280 shall be permitted on each ungrounded overhead 
service conductor. 

230-210. Service Equipment — General Provisions. Ser- 
vice equipment, including instrument transformers, shall 
conform to Article 490, Part A. 

230-211. Metal-Enclosed Switchgear. Metal-enclosed 
switchgear shall consist of a substantial metal structure and 



a sheet metal enclosure. Where installed over a combustible 
floor, suitable protection thereto shall be provided. 

230-212. Services Over 15,000 Volts. Where the voltage 
exceeds 15,000 volts between conductors, they shall enter 
either metal-enclosed switchgear or a transformer vault 
conforming to the requirements of Sections 450-41 through 
450-48. 

Article 240 — Overcurrent Protection 

240-1. Scope. Parts A through G of this article provide the 
general requirements for overcurrent protection and overcur- 
rent protective devices not more than 600 volts, nominal. 
Part H covers overcurrent protection for those portions of 
supervised industrial installations operating at voltages of 
not more than 600 volts, nominal. Part I covers overcurrent 
protection over 600 volts, nominal. 

FPN: Overcurrent protection for conductors and equipment 
is provided to open the circuit if the current reaches a value 
that will cause an excessive or dangerous temperature in 
conductors or conductor insulation. See also Section 110-9 
for requirements for interrupting ratings and Section 110- 
10 for requirements for protection against fault currents. 

A. General 

240-2. Protection of Equipment. Equipment shall be pro- 
tected against overcurrent in accordance with the article in 
this Code that covers the type of equipment as specified in 
the following list: 

Article 

Air-conditioning and refrigerating equipment 440 

Appliances 422 

Audio signal processing, amplification, and 640 

reproduction equipment 

Branch circuits 210 

Busways 364 

Capacitors 460 

Class 1, Class 2, and Class 3 remote-control, 725 

signaling, and power-limited circuits 

Closed-loop and programmed power distribution 780 

Cranes and hoists 610 

Electric signs and outline lighting 600 

Electric welders 630 

Electrolytic cells 668 

Elevators, dumbwaiters, escalators, moving 620 

walks, wheelchair lifts, and stairway chair lifts 

Emergency systems 700 

Fire alarm systems 760 

Fire pumps 695 

Fixed electric heating equipment for pipelines 427 

and vessels 



1999 Edition 



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ARTICLE 240 — OVERCURRENT PROTECTION 



70-71 





Article 


Fixed electric space-heating equipment 


424 


Fixed outdoor electric deicing and snow-melting 


426 


equipment 




Generators 


445 


Health care facilities 


517 


Induction and dielectric heating equipment 


665 


Industrial machinery 


670 


Lighting fixtures, lampholders, lamps, and 


410 


receptacles 




Motion picture and television studios and similar 


530 


locations 




Motors, motor circuits, and controllers 


430 


Phase converters 


455 


Pipe organs 


650 


Places of assembly 


518 


Services 


230 


Solar photovoltaic systems 


690 


Switchboards and panelboards 


384 


Theaters, audience areas of motion picture and 


520 


television studios, and similar locations 




Transformers and transformer vaults 


450 


X-ray equipment 


660 



240-3. Protection of Conductors. Conductors, other than 
flexible cords and fixture wires, shall be protected against 
overcurrent in accordance with their ampacities as specified 

. in Section 310-15, unless otherwise permitted or required 

I in (a) through (g). 

(a) Power Loss Hazard. Conductor overload protection 
shall not be required where the interruption of the circuit 
would create a hazard, such as in a material handling magnet 
circuit or fire pump circuit. Short-circuit protection shall be 
provided. 

FPN: See Standard for the Installation of Centrifugal Fire 
I Pumps, NFPA 20-1996. 

(b) Devices Rated 800 Amperes or Less. The next higher 
standard overcurrent device rating (above the ampacity of 
the conductors being protected) shall be permitted to be 
used, provided all of the following conditions are met. 

(1) The conductors being protected are not part of a multi- 
outlet branch circuit supplying receptacles for cord- and 
plug-connected portable loads. 

(2) The ampacity of the conductors does not correspond 
with the standard ampere rating of a fuse or a circuit 
breaker without overload trip adjustments above its rat- 
ing (but that shall be permitted to have other trip or 
rating adjustments). 

(3) The next higher standard rating selected does not exceed 
800 amperes. 



(c) Devices Rated Over 800 Amperes. Where the overcur- 
rent device is rated over 800 amperes, the ampacity of the 
conductors it protects shall be equal to or greater than the rat- 
ing of the overcurrent device as defined in Section 240-6. 

(d) Small Conductors. Unless specifically permitted in (e) 
through (g), the overcurrent protection shall not exceed 15 
amperes for No. 14, 20 amperes for No. 12, and 30 amperes 
for No. 10 copper; or 15 amperes for No. 12 and 25 amperes 
for No. 10 aluminum and copper-clad aluminum after any 
correction factors for ambient temperature and number of 
conductors have been applied. 

(e) Tap Conductors. Tap conductors shall be permitted to 
be protected against overcurrent in accordance with Sections 
210-19(d), 240-21, 364-11, 364-12, and 430-53(d). . 

As Used in this article, a tap conductor is defined as a 
conductor, other than a service conductor that has overcur- 
rent protection ahead of its point of supply, that exceeds the 
value permitted for similar conductors that are protected as 
described elsewhere in this section. 

(f) Transformer Secondary Conductors. Single-phase 
(other than 2-wire) and multiphase (other than delta-delta, 
3-wire) transformer secondary conductors shall not be con- 
sidered to be protected by the primary overcurrent protective 
device. Conductors supplied by the secondary side of a 
single-phase transformer having a 2-wire (single-voltage) 
secondary, or a three-phase, delta-delta connected trans- 
former having a 3-wire (single- voltage) secondary, shall be 
permitted to be protected by overcurrent protection provided 
on the primary (supply) side of the transformer, provided 
this protection is in accordance with Section 450-3 and does 
not exceed the value determined by multiplying the second- 
ary conductor ampacity by the secondary to primary trans- 
former voltage ratio. 

(g) Overcurrent Protection for Specific Conductor Ap- 
plications. Overcurrent protection for the specific con- 
ductors shall be permitted to be provided as referenced in 
the following list: 

Article Section 

Air-conditioning and 440, Parts C, F 

refrigeration 

equipment circuit 

conductors 
Capacitor circuit 460 460-8(b) and 

conductors 460-25 (a)-(d) 

Control and 727 727-9 

instrumentation 

circuit conductors 

(Type ITC) 
Electric welder circuit 630 630-12 and 

conductors 630-32 



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70-72 



ARTICLE 240 — OVERCURRENT PROTECTION 





Article 


Section 


Fire alarm system 


760 


760-23, 760-24, 


circuit conductors 




760-41, and 
Chapter 9, Tables 
12(a) and 12(b) 


Motor-operated 


422, Part B 




appliance circuit 






conductors 






Motor and motor- 


430, Parts C, 




control circuit 


D, E, F, H 




conductors 






Phase converter 


455. 


455-7 


supply conductors 






Remote-control, 


725 


725-23, 725-24, 


signaling, and 




725-41, and 


power-limited 




Chapter 9, Tables 


circuit conductors 




11(a) and 11(b) 


Secondary tie 


450 


450-6 


conductors 







240-4. Protection of Flexible Cords and Fixture Wires. 

Flexible cord, including tinsel cord and extension cords, and 
fixture wires shall be protected against overcurrent by either 
(a)or(b). 

(a) Ampacities. Flexible cord shall be protected by an ov- 
ercurrent device in accordance with its ampacity as specified 
in Tables 400-5(A) and (B). Fixture wire shall be protected 
against overcurrent in accordance with its ampacity as speci- 
fied in Table 402-5. Supplementary overcurrent protection, 
as in Section 240-10, shall be permitted to be an acceptable 
means for providing this protection. 

(b) Branch Circuit Overcurrent Device. Flexible cord 
shall be protected where supplied by a branch circuit in 
accordance with one of the methods described below. 

(1) Supply Cord of Listed Appliance or Portable 
Lamps. Where flexible cord or tinsel cord is approved for 
and used with a specific listed appliance or portable lamp, 
it shall be permitted to be supplied by a branch circuit of 
Article 210 in accordance with the following: 

20-ampere circuits — tinsel cord or No. 18 cord and 
larger 

30-ampere circuits — No. 16 cord and larger 

40-ampere circuits — cord of 20-ampere capacity and 
over 

50-ampere circuits — cord of 20-ampere capacity and 
over 

(2) Fixture Wire. Fixture wire shall be permitted to be 
tapped to the branch circuit conductor of a branch circuit 
of Article 210 in accordance with the following: 



20-ampere circuits 
run length 



No. 18, up to 50 ft (15.2 m) of 



20-ampere circuits — No. 16, up to 100 ft (30.5 m) of 
run length 

20-ampere circuits — No. 14 and larger 

30-ampere circuits — No. 14 and larger 

40-ampere circuits — No. 12 and larger 

50-ampere circuits — No. 12 and larger 

(3) Extension Cord Sets. Flexible cord used in listed 
extension cord sets, or in extension cords made with sepa- 
rately listed and installed components, shall be permitted to 
be supplied by a branch circuit of Article 210 in accordance 
with the following: 

20-ampere circuits — No. 16 and larger 

240-6. Standard Ampere Ratings. 

(a) Fuses and Fixed-Trip Circuit Breakers. The standard 
ampere ratings for fuses and inverse time circuit breakers 
shall be considered 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 
80, 90, 100, 110, 125, 150, 175, 200, 225, 250, 300, 350, 
400, 450, 500, 600, 700, 800, 1000, 1200, 1600, 2000, 2500, 
3000, 4000, 5000, and 6000 amperes. The use of fuses 
and inverse time circuit breakers with nonstandard ampere 
ratings shall be permitted. The standard ampere rating for 
fuses shall be considered 1, 3, 6, 10, and 601. 

(b) Adjustable-Trip Circuit Breakers. The rating of ad- 
justable-trip circuit breakers having external means for ad- 
justing the current setting (long-time pickup setting), not 
meeting the requirements of (c), shall be the maximum set- 
ting possible. 



(c) Restricted Access Adjustable-Trip Circuit Breakers. 

A circuit breaker(s) that has restricted access to the adjusting 
means shall be permitted to have an ampere rating(s) that 
is equal to the adjusted current setting (long-time pickup 
setting). Restricted access shall be defined as located behind 
one of the following: 

(1) Removable and sealable covers over the adjusting means 

(2) Bolted equipment enclosure doors 

(3) Locked doors accessible only to qualified personnel 

240-8. Fuses or Circuit Breakers in Parallel. Fuses and 
circuit breakers shall be permitted to be connected in parallel 
where they are factory assembled in parallel and listed as a 
unit. Individual fuses, circuit breakers, or combinations 
thereof shall not otherwise be connected in parallel. 



1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 240 — OVERCURRENT PROTECTION 



70-73 



240-9. Thermal Devices. Thermal relays and other devices 
not designed to open short circuits shall not be used for the 
protection of conductors against overcurrent due to short 
circuits or grounds, but the use of such devices shall be 
permitted to protect motor branch-circuit conductors from 
overload if protected in accordance with Section 430-40. 

240-10. Supplementary Overcurrent Protection. Where 
supplementary overcurrent protection is used for lighting 
fixtures, appliances, and other equipment or for internal 
circuits and components of equipment, it shall riot be used 
as a substitute for branch-circuit overcurrent devices or in 
place of the branch-circuit protection specified in Article 
210. Supplementary overcurrent devices shall not be re- 
quired to be readily accessible. 

240-11. Definition of Current-Limiting Overcurrent 
Protective Device. A current-limiting overcurrent protec- 
tive device is a device that, when interrupting currents in its 
current-limiting range, will reduce the current flowing in 
the faulted circuit to a magnitude substantially less than that 
obtainable in the same circuit if the device were replaced 
with a solid conductor having comparable impedance. 

240-12. Electrical System Coordination. Where an or- 
derly shutdown is required to minimize the hazard(s) to 
personnel and equipment, a system of coordination based 
on the following two conditions shall be permitted: 

(1) Coordinated short-circuit protection 

(2) Overload indication based on monitoring systems or 
devices 

For the purposes of this section, coordination is defined 
as properly localizing a fault condition to restrict outages 
to the equipment affected, accomplished by the choice of 
selective fault-protective devices. 

FPN: The monitoring system may cause the condition to go 
to alarm, allowing corrective action or an orderly shutdown, 
thereby minimizing personnel hazard and equipment dam- 
age. 

240-13. Ground-Fault Protection of Equipment. 

Ground-fault protection of equipment shall be provided in 
accordance with the provisions of Section 230-95 for solidly 
grounded wye electrical systems of more than 150 volts to 
ground^ but not exceeding 600 volts phase-to-phase for each 
individual device used as a building or structure main dis- 
connecting means rated 1000 amperes or more. 

The provisions of this section shall not apply to the dis- 
connecting means for the following: 

(1) Continuous industrial processes where a nonorderly 
shutdown will introduce additional or increased hazards 



(2) Installations where ground-fault protection is provided 
by other requirements for services or feeders 

(3) Fire pumps installed in accordance with Article 695 

B. Location 

240-20. Ungrounded Conductors. 

(a) Overcurrent Device Required. A fuse or an over- 
current trip unit of a circuit breaker shall be connected in 
series With each ungrounded conductor. A combination of a 
current transformer and overcurrent relay shall be considered 
equivalent to an overcurrent trip unit. 

FPN: For motor circuits, see Parts C, D, F, and K of Article 
430. 

(b) Circuit Breaker as Overcurrent Device. Circuit 
breakers shall open all ungrounded conductors of the circuit 
unless otherwise permitted in (1), (2), or (3). 

(1) Except where limited by Section 210-4(b), individual 
single-pole circuit breakers, with or without approved handle 
ties, shall be permitted as the protection for each ungrounded 
conductor of multiwire branch circuits that serve only single- 
phase, line-to-neutral loads. 

(2) In grounded systems, individual single-pole circuit 
breakers with approved handle ties shall be permitted as the 
protection for each ungrounded conductor for line-to-line 
connected loads for single-phase circuits or 3-wire, direct- 
current circuits! 

(3) For line-to-line loads in 4-wire, 3-phase systems or 
5-wire, 2-phase systems having a grounded neutral and no 
conductor operating at a voltage greater than permitted in 
Section 210-6, individual single-pole circuit breakers with 
approved handle ties shall be permitted as the protection for 
each ungrounded conductor. 

(c) Closed-Loop Power Distribution Systems. Listed de- 
vices that provide equivalent overcurrent protection in 
closed-loop power distribution systems shall be permitted 
as a substitute for fuses or circuit breakers. 

240-21. Location in Circuit. Overcurrent protection shall 
be provided in each ungrounded circuit conductor and shall 
be located at the point where the conductors receive their 
supply except as specified in (a) through (g). No conductor 
supplied under the provisions of (a) through (g) shall supply 
another conductor under those provisions, except through 
an overcurrent protective device meeting the requirements 
of Section 240-3. 

(a) Branch-Circuit Conductors. Branch-circuit tap con- 
ductors meeting the requirements specified in Section 210-19 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-74 



ARTICLE 240 — OVERCURRENT PROTECTION 



shall be permitted to have overcurrent protection located as 
specified in that Section. 

(b) Feeder Taps. Conductors shall be permitted to be 
tapped, without overcurrent protection at the tap, to a feeder 
as specified in (1) through (5). 

(1) Taps Not Over 10 ft (3.05 m) Long. Where the 
length of the tap conductors does not exceed 10 ft (3.05 m) 
and the tap conductors comply with all of the following. 

(a) The ampacity of the tap conductors is 

(1) Not less than the combined computed loads on the 
circuits supplied by the tap conductors, and 
I (2) Not less than the rating of the device supplied by 
the tap conductors or not less than the rating of the 
overcurrent-protective device at the termination of 
the tap conductors. 

I (b) The tap conductors do not extend beyond the switch- 
board, panelboard, disconnecting means, or control de- 
vices they supply. 

I (c) Except at the point of connection to the feeder, the tap 
conductors are enclosed in a raceway, which shall extend 
from the tap to the enclosure of an enclosed switchboard, 
panelboard, or control devices, or to the back of an open 
switchboard. 

I (d) For field installations where the tap conductors leave 
the enclosure or vault in which the tap is made, the 
rating of the overcurrent device on the line side of the 
tap conductors shall not exceed 10 times the ampacity 
of the tap conductor. 

I FPN: For overcurrent protection requirements for lighting 
and appliance branch-circuit panelboards, see Sections 384- 
16(a) and (e). 

I (2) Taps Not Over 25 ft (7.62 m) Long. Where the 
length of the tap conductors does not exceed 25 ft (7.62 rri) 
and the tap conductors comply with all of the following. 

(a) The ampacity of the tap conductors is not less than one- 
third of the rating of the overcurrent device protecting 
the feeder conductors. 

(b) The tap conductors terminate in a single circuit breaker 
or a single set of fuses that will limit the load to the 
ampacity of the tap conductors. This device shall be 
permitted to supply any number of additional over- 
current devices on its load side. 

(c) The tap conductors are suitably protected from physical 
damage or are enclosed in a raceway. 

(3) Taps Supplying a Transformer [Primary Plus Sec- 
ondary Not Over 25 ft (7.62 m) Long]. Where the tap 
conductors supply a transformer and comply with all the 
following conditions. 



(a) The conductors supplying the primary of a transformer 
have an ampacity at least one-third of the raiting of the 
overcurrent device protecting the feeder conductors. 

(b) The conductors supplied by the secondary of the trans- 
former shall have an ampacity that, when multiplied by 
the ratio of the secondary-to-primary voltage, is at least 
one-third of the rating of the overcurrent device protect- 
ing the feeder conductors. 

(c) The total length of one primary plus one secondary 
conductor, excluding any portion of the primary conduc- 
tor that is protected at its ampacity, is not over 25 ft 
(7.62 m). 

(d) The primary and secondary conductors are suitably pro- 
tected from physical damage. 

(e) The secondary conductors terminate in a single circuit 
breaker or set of fuses that will limit the load current 
to not more than the conductor ampacity that is permitted 
by Section 310-15. 

(4) Taps Over 25 ft (7.62 m) Long. Where the feeder 
is in a high bay manufacturing building over 35 ft (10.67 m) 
high at walls, and the installation complies with all of the 
following conditions. 

(a) Conditions of maintenance and supervision ensure that 
only qualified persons will service the systems. 

(b) The tap conductors are not over 25 ft (7.62 m) long 
horizontally and not over 100 ft (30.5 m) total length. 

(c) The ampacity of the tap conductors is not less than one- 
third of the rating of the overcurrent device protecting 
the feeder conductors. 

(d) The tap conductors terminate at a single circuit breaker 
or a single set of fuses that will limit the load to the 
ampacity of the tap conductors. This single overcurrent 
device shall be permitted to supply any number of addi- 
tional overcurrent devices on its load side. 

(e) The tap conductors are suitably protected from physical 
damage or are enclosed in a raceway. 

(f) The tap conductors are continuous from end-to-end and 
contain no splices. 

(g) The tap conductors are sized No. 6 copper or No. 4 
aluminum or larger. 

(h) The tap conductors do not penetrate walls, floors, or 

ceilings, 
(i) The tap is made no less than 30 ft (9.14 m) from the 

floor. 

(5) Outside Taps of Unlimited Length. Where the con- 
ductors are located outdoors, except at the point of termi- 
nation, and comply with all of the following conditions. 

(a) The conductors are suitably protected from physical 
damage. 

(b) The conductors terminate at a single circuit breaker or 
a single set of fuses that will limit the load to the ampac- 



• 



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ARTICLE 240 — OVERCURRENT PROTECTION 



70-75 



ity of the conductors. This single overcurrent device 
shall be permitted to supply any number of additional 
overcurrent devices on its load side. 

(c) The overcurrent device for the conductors is an integral 
part of a disconnecting means or shall be located imme- 
diately adjacent thereto. 

(d) The disconnecting means for the conductors is installed 
at a readily accessible location either outside of a build- 
ing or structure, or inside nearest the point of entrance 
of the conductors. 

(c) Transformer Secondary Conductors. Conductors 
shall be permitted to be connected to a transformer second- 
ary, without overcurrent protection at the secondary, as speci- 
fied in (1) through (4). 

FPN: For overcurrent protection requirements for trans- 
formers, see Section 450-3. 

(1) Protection by Primary Overcurrent Device. Sin- 
gle-phase (other than 2-wire) and multiphase (other than 
delta-delta, 3 -wire) transformer secondary conductors are 
not considered to be protected by the primary overcurrent 
protective device. Conductors supplied by the secondary 
side of a single-phase transformer having a 2-wire (single- 
voltage) secondary, or a three-phase, delta-delta connected 
transformer having a 3 -wire (single- voltage) secondary, shall 
be permitted to be protected by overcurrent protection pro- 
vided on the primary (supply) side of the transformer, pro- 
vided this protection is in accordance with Section 450-3 
and does not exceed the value determined by multiplying the 
secondary conductor ampacity by the secondary to primary 
transformer voltage ratio. 

(2) Transformer Secondary Conductors Not Over 10 
ft (3.05 m) Long. Where the length of secondary conductor 
does not exceed 10 ft (3.05 m) and complies with all of the 
following. 

(a) The ampacity of the secondary conductors is 

(1) Not less than the combined computed loads on the 
circuits supplied by the secondary conductors, and 

(2) Not less than the rating of the device supplied by 
the secondary conductors or not less than the rating 
of the overcurrent-protective device at the termina- 
tion of the secondary conductors. 

(b) The secondary conductors do not extend beyond the 
switchboard, panelboard, disconnecting means, or con- 
trol devices they supply. 

(c) The secondary conductors are enclosed in a raceway, 
which shall extend from the transformer to the enclosure 
of an enclosed switchboard, panelboard, or control de- 
vices, or to the back of an open switchboard. 



FPN: For overcurrent protection requirements for lighting 
and appliance branch-circuit panelboards, see Sections 384- 
16(a) and (e). 

(3) Secondary Conductors Not Over 25 ft (7.62 m) 
Long. For industrial installations only, where the length of 
the secondary conductors does not exceed 25 ft (7.62 m) 
and complies with all of the following. 

(a) The ampacity of the secondary conductors is not less 
than the secondary current rating of the transformer, and 
the sum of the ratings of the overcurrent devices does 
not exceed the ampacity of the secondary conductors. 

(b) All overcurrent devices are grouped. 

(c) The secondary conductors are suitably protected from 
physical damage. 

(4) Outside Secondary Conductors. Where the con- 
ductors are located outdoors, except at the point of termi- 
nation, and comply with all of the following conditions. 

(a) The conductors are suitably protected from physical 
damage. 

(b) The conductors terminate in an overcurrent device that 
will limit the load to the ampacity of the conductors. 
The overcurrent device shall be permitted to consist of 
not more than six curcuit breakers or six sets of fuses 
grouped in one location. 

(c) The overcurrent device for the conductors is an integral 
part of a disconnecting means or shall be located imme- 
diately adjacent thereto. 

(d) The disconnecting means for the conductors- are installed 
at a readily accessible location either outside of a build- 
ing or structure, or inside nearest the point of entrance 
of the conductors. 

(5) Secondary Conductors from a Feeder Tapped 
Transformer. Transformer secondary conductors installed 
in accordance with Section 240-2 1(b)(3) shall be permitted 
to have overcurrent protection as specified in that section. 

(d) Service Conductors. Service-entrance conductors shall 
be permitted to be protected by overcurrent devices in accor- 
dance with Section 230-91. 

(e) Busway Taps. Busways and busway taps shall be per- 
mitted to be protected against overcurrent in accordance 
with Sections 364-10 through 364-13. 

(f) Motor Circuit Taps. Motor-feeder and branch-circuit 
conductors shall be permitted to be protected against over- 
current in accordance with Sections 430-28 and 430-53 re- 
spectively. 

(g) Conductors from Generator Terminals. Conductors 
from generator terminals that meet the size requirement in 
Section 445-5 shall be permitted to be protected against 



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70-76 



ARTICLE 240 — OVERCURRENT PROTECTION 



overload by the generator overload protective device(s) re- 
quired by Section 445-4. 

240-22. Grounded Conductor. No overcurrent device 
shall be connected in series with any conductor that is inten- 
tionally grounded, unless one of the following two conditions 
are met: 

(1) The overcurrent device opens all conductors of the cir- 
cuit, including the grounded conductor, and is designed 
so that no pole can operate independently 

(2) Where required by Sections 430-36 or 430-37 for motor 
overload protection 

240-23. Change in Size of Grounded Conductor. Where 
a change occurs in the size of the ungrounded conductor, a 
similar change shall be permitted to be made in the size of 
the grounded conductor. 

240-24. Location in or on Premises. 

(a) Accessibility. Overcurrent devices shall be readily ac- 
cessible unless one of the following applies. 



(e) Not Located in Bathrooms. In dwelling units and guest 
rooms of hotels and motels, overcurrent devices, other than 
supplementary overcurrent protection, shall not be located 
in bathrooms as defined in Article 100. 



C. Enclosures 
240-30. General. 

(a) Overcurrent devices shall be protected from physical 
damage by one of the following: 

(1) Installation in enclosures, cabinets, cutout boxes, or 
equipment assemblies 

(2) Mounting on open-type switchboards, panelboards, or 
control boards that are in rooms or enclosures free from 
dampness and easily ignitible material, and are accessi- 
ble only to qualified personnel 



(b) The operating handle of a circuit breaker shall be per- 
mitted to be accessible without opening a door or cover. 



• 



(1) For busways, as provided in Section 364-12. 

(2) For supplementary overcurrent protection, as described 
in Section 240-10. 

(3) For overcurrent devices, as described in Sections 225- 
40 and 230-92. 

(4) For overcurrent devices adjacent to utilization equip- 
ment that they supply, access shall be permitted to be 
by portable means. 

(b) Occupancy. Each occupant shall have ready access to 
all overcurrent devices protecting the conductors supplying 
that occupancy. Where electric service and electrical mainte- 
nance are provided by the building management and where 
these are under continuous building management supervi- 
sion, the service overcurrent devices and feeder overcurrent 
devices supplying more than one occupancy shall be permit- 
ted to be accessible to only authorized management person- 
nel in the following: 

(1) In multiple occupancy buildings 

(2) For guest rooms of hotels and motels that are intended 
for transient occupancy 

(c) Not Exposed to Physical Damage. Overcurrent de- 
vices shall be located where they will not be exposed to 
physical damage. 

FPN: See Section 110-11, Deteriorating Agents. 

(d) Not in Vicinity of Easily Ignitible Material. Overcur- 
rent devices shall not be located in the vicinity of easily 
ignitible material, such as in clothes closets. 



240-32. Damp or Wet Locations. Enclosures for over- 
current devices in damp or wet locations shall comply with 
Section 373-2(a). 

240-33. Vertical Position. Enclosures for overcurrent de- 
vices shall be mounted in a vertical position. Circuit breaker 
enclosures shall be permitted to be installed horizontally 
where the circuit breaker is installed in accordance with 
Section 240-81. Listed busway plug-in units shall be permit- 
ted to be mounted in orientations corresponding to the bus- 
way mounting position. 



D. Disconnecting and Guarding 

240-40. Disconnecting Means for Fuses. A disconnecting 
means shall be provided on the supply side of all fuses in 
circuits over 150 volts to ground and cartridge fuses in 
circuits of any voltage where accessible to other than quali- 
fied persons so that each individual circuit containing fuses 
can be independently disconnected from the source of power. 
A current- limiting device without a disconnecting means 
shall be permitted on the supply side of the sendee discon- 
necting means as permitted by Section 230-82. A single 
disconnecting means shall be permitted on the supply side 
of more than one set of fuses as permitted by Section 430- 
112, Exception, for group operation of motors and Section 
424-22(c) for fixed electric space-heating equipment. 

240-41. Arcing or Suddenly Moving Parts. Arcing or 
suddenly moving parts shall comply with (a) and (b). 



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ARTICLE 240 — OVERCURRENT PROTECTION 



70-77 



(a) Location. Fuses and circuit breakers shall be located 
or shielded so that persons will not be burned or otherwise 
injured by their operation. 

(b) Suddenly Moving Parts. Handles or levers of circuit 
breakers, and similar parts that may move suddenly in such 
a way that persons in the vicinity are likely to be injured 
by being struck by them, shall be guarded or isolated. 

E. Plug Fuses, Fuseholders, and Adapters 
240-50. General. 

(a) Maximum Voltage. Plug fuses shall be permitted to be 
used in the following circuits: 

(1) Circuits not exceeding 125 volts between conductors 

(2) Circuits supplied by a system having a grounded neutral 
where the line-to-neutral voltage does not exceed 150 
volts 

(b) Marking. Each fuse, fuseholder, and adapter shall be 
marked with its ampere rating. 

(c) Hexagonal Configuration. Plug fuses of 15 -ampere 
and lower rating shall be identified by a hexagonal configura- 
tion of the window, cap, or other prominent part to distin- 
guish them from fuses of higher ampere ratings. 

(d) No Energized Parts. Plug fuses, fuseholders, and 
adapters shall have no exposed energized parts after fuses 
or fuses and adapters have been installed. 

(e) Screw Shell. The screw shell of a plug-type fuseholder 
shall be connected to the load side of the circuit. 

240-51. Edison-Base Fuses. 

(a) Classification. Plug fuses of the Edison-base type shall 
be classified at not over 125 volts and 30 amperes and below. 

(b) Replacement Only. Plug fuses of the Edison-base type 
shall be used only for replacements in existing installations 
where there is no evidence of overfusing or tampering. 

240-52. Edison-Base Fuseholders. Fuseholders of the Ed- 
ison-base type shall be installed only where they are made 
to accept Type S fuses by the use of adapters. 

240-53. Type S Fuses. Type S fuses shall be of the plug 
type and shall comply with (a) and (b). 

(a) Classification. Type S fuses shall be classified at not 
over 125 volts and to 15 amperes, 16 to 20 amperes, and 
21 to 30 amperes. 



(b) Noninterchangeable. Type S fuses of an ampere classi- 
fication as specified in (a) shall not be interchangeable with 
a lower ampere classification. They shall be designed so 
that they cannot be used in any fuseholder other than a 
Type S fuseholder or a fuseholder with a Type S adapter 
inserted. 

240-54. Type S Fuses, Adapters, and Fuseholders. 

(a) To Fit Edison-Base Fuseholders. Type S adapters shall 
fit Edison-base fuseholders. 

(b) To Fit Type S Fuses Only. Type S fuseholders and 
adapters shall be designed so that either the fuseholder itself 
or the fuseholder with a Type S adapter inserted cannot be 
used for any fuse other than a Type S fuse. 

(c) Nonremovable. Type S adapters shall be designed so 
that once inserted in a fuseholder, they cannot be removed. 

(d) Nontamperable. Type S fuses, fuseholders, and adapt- 
ers shall be designed so that tampering or shunting (bridging) 
would be difficult. 

(e) Interchangeability. Dimensions of Type S fuses, fuse- 
holders, and adapters shall be standardized to permit inter- 
changeability regardless of the manufacturer. 

F. Cartridge Fuses and Fuseholders 
240-60. General. 

(a) Maximum Voltage — 300- Volt Type. Cartridge fuses 
and fuseholders of the 300-volt type shall be permitted to 
be used in the following circuits: 

(1) Circuits not exceeding 300 volts between conductors 

(2) Single-phase line-to-neutral circuits supplied from a 3- 
phase, 4-wire, solidly grounded neutral source where 
the line-to-neutral voltage does not exceed 300 volts 

(b) Noninterchangeable — 0-6000-Ampere Cartridge 
Fuseholders. Fuseholders shall be designed so that it will 
be difficult to put a fuse of any given class into a fuseholder 
that is designed for a current lower, or voltage higher, than 
that of the class to which the fuse belongs. Fuseholders for 
current-limiting fuses shall not permit insertion of fuses that 
are not current limiting. 

(c) Marking. Fuses shall be plainly marked, either by print- 
ing on the fuse barrel or by a label attached to the barrel 
showing the following: 

(1) Ampere rating 

(2) Voltage rating 

(3) Interrupting rating where other than 10,000 amperes 

(4) Current limiting where applicable 

(5) The name or trademark of the manufacturer 



NATIONAL ELECTRICAL CODE 



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70-78 



ARTICLE 240 — OVERCURRENT PROTECTION 



The interrupting rating shall not be required to be marked 
on fuses used for supplementary protection. 



that is indicative of their capability to interrupt fault currents 
between phases or phase to ground. 



240-61. Classification. Cartridge fuses and fuseholders 
shall be classified according to voltage and amperage ranges. 
Fuses rated 600 volts, nominal or less, shall be permitted 
to be used for voltages at or below their ratings. 



G. Circuit Breakers 

240-80. Method of Operation. Circuit breakers shall be 
trip free and capable of being closed and opened by manual 
operation. Their normal method of operation by other than 
manual means, such as electrical or pneumatic, shall be 
permitted if means for manual operation is also provided. 

240-81. Indicating. Circuit breakers shall clearly indicate 
whether they are in the open "off or closed "on" position. 
Where circuit breaker handles are operated vertically 
rather than rotationally or horizontally, the "up" position of 
the handle shall be the "on" position. 

240-82. Nontamperable. A circuit breaker shall be of such 
design that any alteration of its trip point (calibration) or 
the time required for its operation will require dismantling 
of the device or breaking of a seal for other than intended 
adjustments. 

240-83. Marking. 

(a) Durable and Visible. Circuit breakers shall be marked 
with their ampere rating in a manner that will be durable 
and visible after installation. Such marking shall be permitted 
to be made visible by removal of a trim or cover. 

(b) Location. Circuit breakers rated at 100 amperes or less 
and 600 volts or less shall have the ampere rating molded, 
stamped, etched, or similarly marked into their handles or 
escutcheon areas. 

(c) Interrupting Rating. Every circuit breaker having an 
interrupting rating other than 5000 amperes shall have its 
interrupting rating shown on the circuit breaker. The inter- 
rupting rating shall not be required to be marked on circuit 
breakers used for supplementary protection. 

(d) Used as Switches. Circuit breakers used as switches in 
120- volt and 27 7 -volt fluorescent lighting circuits shall be 
listed and shall be marked "SWD." 

(e) Voltage Marking. Circuit breakers shall be marked 
with a voltage rating not less than the nominal system voltage 



240-85. Applications. A circuit breaker with a straight 
voltage rating, such as 240V or 480V, shall be permitted to 
be applied in a circuit in which the nominal voltage between 
any two Conductors does not exceed the circuit breaker's 
voltage rating. A two-pole circuit breaker shall not be used 
for protecting a 3-phase, corner-grounded delta circuit unless 
the circuit breaker is marked l(J>-3(j) to indicate such suitabil- 
ity. . 

A circuit breaker with a slash rating, such as 120/240V 
or 480Y/277V, shall be permitted to be applied in a circuit 
where the nominal voltage of any conductor to ground does 
not exceed the lower of the two values of the circuit breaker's 
voltage rating and the nominal voltage between any two 
conductors does not exceed the higher value of the circuit 
breaker's voltage rating. 

240-86. Series Ratings. Where a circuit breaker is used on 
a circuit having an available fault current higher than its 
marked interrupting rating by being connected on the load 
side of an acceptable overcurrent protective device having 
the higher rating, the following shall apply. 

(a) Marking. The additional series combination inter- 
rupting rating shall be marked on the end use equipment, 
such as switchboards and panelboards. 

(b) Motor Contribution. Series ratings shall not be used 
where 



(1) Motors are connected on the load side of the higher- 
rated overcurrent device and on the line side of the 
lower-rated overcurrent device. 

(2) The sum of the motor full-load currents exceeds 1 per- 
cent of the interrupting rating of the lower-rated circuit 
breaker. 



H. Supervised Industrial Installations 

240-90. General. Overcurrent protection in areas of super- 
vised industrial installations shall comply with all the appli- 
cable provisions of the other sections of this article, except 
as provided in Part H. The provisions of Part H shall only 
be permitted to apply to those portions of the electrical 
system in the supervised industrial installation used exclu- 
sively for manufacturing or process control activities. 



240-91. Definition of Supervised Industrial Installa- 
tion. For the purposes of Part H, supervised industrial in- 



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ARTICLE 240 — OVERCURRENT PROTECTION 



70-79 



stallation is defined as the industrial portions of a facility 
where all of the following conditions are met. 

(1) Conditions of maintenance and engineering supervision 
ensure that only qualified persons will monitor and ser- 
vice the system. 

(2) The premises wiring system has 2500 kVA or greater 
of load used in industrial process(es), manufacturing 
activities, or both, as calculated in accordance with Arti- 
cle 220. 

(3) The premises has at least one service that is more than 
150 volts to ground and more than 300 volts phase-to- 
phase. 

This definition shall not apply to those installations in 
buildings used by the industrial facility for offices, ware- 
houses, garages, machine shops, and recreational facilities 
that are not an integral part of the industrial plant, substation, 
or control center. 

240-92. Location in Circuit. An overcurrent device shall 
be connected in each ungrounded circuit conductor as fol- 
lows. 

(a) Feeder and Branch-Circuit Conductors. Feeder and 
branch-circuit conductors shall be protected at the point the 
conductors receive their supply, as permitted in Section 
240-21, or as otherwise permitted in (b) or (c). 

(b) Transformer Secondary Conductors of Separately 
Derived Systems. Conductors shall be permitted to be con- 
nected to a transformer secondary of a separately derived 
system, without overcurrent protection at the connection, 
where the conditions of (1), (2), and (3) are met. 

(1) Short-Circuit and Ground-Fault Protection. The 

conductors shall be protected from short-circuit and ground- 
fault conditions by complying with one of the following 
conditions. 

(a) The length of the secondary conductors does not exceed 
50 ft (15.24 m) and the transformer primary overcurrent 
device has a rating or setting that does not exceed 150 
percent of the value determined by multiplying the sec- 
ondary conductor ampacity by the secondary-to-primary 
transformer voltage ratio. 

(b) The length of the secondary conductors does not exceed 
75 ft (22.86 m) and the conductors are protected by a 
differential relay with a trip setting equal to or less than 
the conductor ampacity. 

(c) The conductors shall be considered to be protected if 
the length of the secondary conductors does not exceed 
75 ft (22.86 m) and if calculations, made under engi- 
neering supervision, determine that the system over- 
current devices will protect the conductors within 



recognized time vs. current limits for all short-circuit 
and ground-fault conditions. 

(2) Overload Protection. The conductors shall be pro- 
tected against overload conditions by complying with one 
of the following. 



(a) The conductors terminate in a single overcurrent device 
that will limit the load to the conductor ampacity. 

(b) The sum of the overcurrent devices at the conductor 
termination limits the load to the conductor ampacity. 
The overcurrent devices shall consist of not more than 
six circuit breakers or sets of fuses, mounted in a single 
enclosure, in a group of separate enclosures, or in or on a 
switchboard. There shall be no more than six overcurrent 
devices grouped in any one location. 

(c) Overcurrent relaying is connected [with a current trans- 
formers), if needed] to sense all of the secondary con- 
ductor current and limit the load to the conductor 
ampacity by opening upstream or downstream devices. 

(d) Conductors shall be considered to be protected if calcu- 
lation's, made under engineering supervision, determine 
that the system overcurrent devices will protect the con- 
ductors from overload conditions. 

(3) Physical Protection. The secondary conductors 
shall be suitably protected from physical damage. 

(c) Outside Feeder Taps. Outside conductors shall be per- 
mitted to be tapped to a feeder or to be connected at a 
transformer secondary, without overcurrent protection at the 
tap or connection, where all the following conditions are 
met. 



(1) The conductors are suitably protected from physical 
damage. 

(2) The sum of the overcurrent devices at the conductor 
termination limits the load to the conductor ampacity. 
The overcurrent devices shall consist of not more than 
six circuit breakers or sets of fuses mounted in a single 
enclosure, in a group of separate enclosures, or in or on a 
switchboard. There shall be no more than six overcurrent 
devices grouped in any one location. 

(3) The tap conductors are installed outdoors, except at the 
point of termination. 

(4) The overcurrent device for the conductors is an integral 
part of a disconnecting means or shall be located imme- 
diately adjacent thereto. 

(5) The disconnecting means for the conductors are installed 
at a readily accessible location either outside of a build- 
ing or structure or inside nearest the point of entrance 
of the conductors. 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-80 



ARTICLE 250 — GROUNDING 



I. Overcurrent Protection Over 600 Volts, Nominal 
240-100. Feeders and Branch Circuits. 

(a) Feeder and branch-circuit conductors shall have over- 
current protection in each ungrounded conductor located at 
the point where the conductor receives its supply or at a 
location in the circuit determined under engineering supervi- 
sion. The overcurrent protection shall be permitted to be 
provided by one of the following. 

(1) Overcurrent Relays and Current Transformers. 

Circuit breakers used for overcurrent protection of 3-phase 
circuits shall have a minimum of three overcurrent relays 
operated from three current transformers. On 3-phase, 3- 
wire circuits, an overcurrent relay in the residual circuit of 
the current transformers shall be permitted to replace one 
of the phase relays. 

An overcurrent relay, operated from a current transformer 
that links all phases of a 3-phase, 3 -wire circuit, shall be 
permitted to replace the residual relay and one of the phase- 
conductor current transformers. Where the neutral is not 
regrounded on the load side of the circuit as permitted in 
Section 250- 184(b), the current transformer shall be permit- 
ted to link all 3-phase conductors and the grounded circuit 
conductor (neutral). 

(2) Fuses. A fuse shall be connected in series with each 
ungrounded conductor. 

(b) Protective Devices. The protective device(s) shall be 
capable of detecting and interrupting all values of current 
that can occur at their location in excess of their trip setting 
or melting point. 

(c) Conductor Protection. The operating time of the pro- 
tective device, the available short-circuit current, and the 
conductor used shall be coordinated to prevent damaging or 
dangerous temperatures in conductors or conductor insula- 
tion under short-circuit conditions. 

240-101. Additional Requirements for Feeders. 

(a) Rating or Setting of Overcurrent Protective Devices. 

The continuous ampere rating of a fuse shall not exceed 
three times the ampacity of the conductors. The long-time 
trip element setting of a breaker or the minimum trip setting 
of an electronically actuated fuse shall not exceed six times 
the ampacity of the conductor. For fire pumps, conductors 
shall be permitted to be protected for overcurrent in accor- 
dance with Section 695-4(b). 

(b) Feeder Taps. Conductors tapped to a feeder shall be 
permitted to be protected by the feeder overcurrent device 

1 where that overcurrent device also protects the tap conductor. 



Article 250 — Grounding 

See Appendix E for a cross reference list of section numbers 
between the 1996 Article 250 and the 1999 Article 250. 



A. General 

250-1. Scope. This article covers general requirements for 
grounding and bonding of electrical installations, and spe- 
cific requirements in (1) through (6). 

(1) Systems, circuits, and equipment required, permitted, or 
not permitted to be grounded 

(2) Circuit conductor to be grounded on grounded systems 

(3) Location of grounding connections 

(4) Types and sizes of grounding and bonding conductors 
and electrodes 

(5) Methods of grounding and bonding 

(6) Conditions under which guards, isolation, or insulation 
may be substituted for grounding 

250-2. General Requirements for Grounding and Bond- 
ing. The following general requirements identify what 
grounding and bonding of electrical systems are required to 
accomplish. The prescriptive methods contained in Article 
250 shall be followed to comply with the performance re- 
quirements of this section. . » 

(a) Grounding of Electrical Systems. Electrical systems 
that are required to be grounded shall be connected to earth 
in a manner that will limit the voltage imposed by lightning, 
line surges, or unintentional contact with higher voltage lines 
and that will stabilize the voltage to earth during normal 
operation. 

(b) Grounding of Electrical Equipment. Conductive ma- 
terials enclosing electrical conductors or equipment, or form- 
ing part of such equipment, shall be connected to earth so 
as to limit the voltage to ground on these materials. Where 
the electrical system is required to be grounded, these mate- 
rials shall be connected together and to the supply system 
grounded conductor as specified by this article. Where the 
electrical system is not solidly grounded, these materials 
shall be connected together in a manner that establishes an 
effective path for fault current. > 

(c) Bonding of Electrically Conductive Materials and 
Other Equipment. Electrically conductive materials, such 
as metal water piping, metal gas piping, and structural steel 
members, that are likely to become energized shall be bonded 
as specified by this article to the supply system grounded 
conductor or, in the case of an ungrounded electrical system, 
to the electrical system grounded equipment, in a manner 
that establishes an effective path for fault current. 



1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 250 — GROUNDING 



70-81 



(d) Performance of Fault Current Path. The fault current 
path shall be permanent and electrically continuous, shall 
be capable of safely carrying the maximum fault likely to 
be imposed on it, and shall have sufficiently low impedance 
to facilitate the operation of overcurrent devices under fault 
conditions. 

The earth shall not be used as the sole equipment ground- 
ing conductor or fault current path. 

FPN: See Figure 250-2 for information on the organization 
of Article 250. 



Part A. General 



Part B. Circuit and 
system grounding 



Part H. Direct-current 
systems. 



Part K. Grounding of 

systems and circuits of 

1 kV and over (high voltage) 



Part C. Grounding electrode 

system and grounding 

electrode conductor 



Part D. Enclosure, 

raceway, and service 

cable grounding 



Part F. Equipment 

grounding and equipment 

grounding conductors 




Part E. Bonding 



Part G. Methods of 
equipment grounding 



Part J. Instruments, 
meters, and relays 



Figure 250-2 Grounding. 

250-4. Application of Other Articles. In other articles 
applying to particular cases of installation of conductors and 
equipment, there are requirements that are in addition to 
those of this article or are modifications of them. 



Article 



Agricultural buildings 
Audio signal processing, 
amplification, and 
reproduction equipment 



Section 

547-8 
640-7 



Article 



Branch circuits 



Cablebus 
Capacitors 

Circuits and equipment 

operating at less than 

50 volts 
Class 1, Class 2, and Class 3 

remote-control, signaling, and 

power-limited circuits 
Closed-loop and programmed 

power distribution 
Communications circuits 



Flexible cords and cables 
Floating buildings 



Grounding-type receptacles, 
adapters, cord connectors, and 
attachment plugs 

Hazardous (classified) locations 

Health care facilities 



720 



800 



500-517 

517 



Section 

210-5 
210-6 
210-7 
365-9 
460-10 
460-27 



725-6 



780-3 



Community antenna television 




820-33 


and radio distribution systems 




820-40 
820-41 


Conductors for general wiring 


310 




Cranes and hoists 


610 




Electrically driven or controlled 




675-1 1(c) 


irrigation machines 




675-12 
675-13 
675-14 
675-15 


Electric signs and outline 


600 




lighting 






Electrolytic cells 


668 




Elevators, dumbwaiters, 


620 




escalators, moving walks, 






wheelchair lifts, and stairway 






chair lifts 






Fire alarm systems 




760-6 


Fixed electric heating equipment 




427-29 


for pipelines and vessels 




427-48 


Fixed outdoor electric deicing 




426-27 


and snow-melting equipment 






Fixtures and lighting equipment 




410-17 



410-18 
410-20 
410-21 
410-105(b) 
400-22 
400-23 
553-8 
553-10 
553-11 
410-58 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-82 



ARTICLE 250 — GROUNDING 



Induction and dielectric heating 

equipment 
Industrial machinery 
Information technology 

equipment 
Intrinsically safe systems 
Lighting fixtures, lampholders, 

lamps, and receptacles 
Marinas and boatyards 
Mobile homes and mobile home 

park 
Motion picture and television 

studios and similar locations 
Motors, motor circuits, and 

controllers 
Outlet, device, pull and junction 

boxes, conduit bodies and 

fittings 
Over 600 volts, nominal, 

underground wiring methods 
Panelboards 
Pipe organs 

Radio and television equipment 
Receptacles and cord connectors 
Recreational vehicles and 

recreational vehicle parks 
Services 
Solar photovoltaic systems 



Swimming pools, fountains, and 

similar installations 
Switchboards and panelboards 
Switches 
Theaters, audience areas of 

motion picture and television 

studios, and similar locations 
Transformers and transformer 

vaults 
Use and identification of 

grounded conductors 
X-ray equipment 



Article 

665 

670 



410 



550 



430 



650 
810 

551 

230 



680 



200 
660 



Section 

645-15 
504-50 

555-8 



530-20 
530-66 



370-4 
370-25 

300-50(b) 

384-20 

210-7 



690-41 
690-42 
690-43 
690-45 
690-47 



384-3(d) 

380-12 

520-81 



450-10 



517-78 



250-6. Objectionable Current Over Grounding Con- 
ductors. 

(a) Arrangement to Prevent Objectionable Current. 

The grounding of electrical systems, circuit conductors, 
surge arresters, and conductive noncurrent-carrying materi- 
als and equipment shall be installed and arranged in a manner 



that will prevent an objectionable flow of current over the 
grounding conductors or grounding paths. 

(b) Alterations to Stop Objectionable Current. If the use 

of multiple grounding connections results in an objectionable 
flow of current, one or more of the following alterations 
shall be permitted to be made, provided that the requirements 
of Section 250-2(d) are met. 

(1) Discontinue one or more but not all of such grounding 
connections. 

(2) Change the locations of the grounding connections. 

(3) Interrupt the continuity of the conductor or conductive 
path interconnecting the grounding connections. 

(4) Take other suitable remedial action satisfactory to the 
authority having jurisdiction. 

(c) Temporary Currents Not Classified as Objectionable 
Currents. Temporary currents resulting from accidental 
conditions, such as ground-fault currents, that occur only 
while the grounding conductors are performing their in- 
tended protective functions shall not be classified as objec- 
tionable current for the purposes specified in' (a) and (b). 

(d) Limitations to Permissible Alterations. The provi- 
sions of this section shall not be considered as permitting 
electronic equipment from being operated on ac systems or 
branch circuits that are not grounded as required by this 
article. Currents that introduce noise or data errors in elec- 
tronic equipment shall not be considered the objectionable 
currents addressed in this section. 

(e) Isolation of Objectionable Direct-Current Ground 
Currents. Where isolation of objectionable dc ground cur- 
rents from cathodic protection systems is required, a listed 
ac coupling/dc isolating device shall be permitted in the 
equipment grounding path to provide an effective return path 
for ac ground-fault current while blocking dc current. 

250-8. Connection of Grounding and Bonding Equip- 
ment. Grounding conductors and bonding jumpers shall be 
connected by exothermic welding, listed pressure connec- 
tors, listed clamps, or other listed means. Connection devices 
or fittings that depend solely on solder shall not be used. 
Sheet metal screws shall not be used to connect grounding 
conductors to enclosures. 

250-10. Protection of Ground Clamps and Fittings. 

Ground clamps or other fittings shall be approved for general 
use without protection or shall be protected from physical 
damage as indicated in (1) or (2). 

(1) In installations where they are not likely to be damaged 

(2) Where enclosed in metal, wood, or equivalent protective 
covering 



1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 250 — GROUNDING 



70-83 



250-12. Clean Surfaces. Nonconductive coatings (such as 
paint, lacquer, and enamel) on equipment to be grounded 
shall be removed from threads and other contact surfaces to 
ensure good electrical continuity or be connected by means 
of fittings designed so as to make such removal unnecessary. 

B. Circuit and System Grounding 

250-20. Alternating-Current Circuits and Systems to Be 
Grounded. Alternating-current circuits and systems shall 
be grounded as provided for in (a), (b), (c), or (d). Other 
circuits and systems shall be permitted to be grounded. 

FPN: An example of a system permitted to be grounded is 
a corner-grounded delta transformer connection. See Section 
250-26(4) for conductor to be grounded. 

(a) Alternating-Current Circuits of Less than 50 Volts. 

Alternating-current circuits of less than 50 volts shall be 
grounded under any of the following conditions: 

(1) Where supplied by transformers, if the transformer sup- 
ply system exceeds 150 volts to ground 

(2) Where supplied by transformers, if the transformer sup- 
ply system is ungrounded 

(3) Where installed as overhead conductors outside of build- 
ings 

(b) Alternating-Current Systems of 50 Volts to 1000 Volts. 

Alternating-current systems of 50 volts to 1000 volts that 
supply premises wiring and premises wiring systems shall 
be grounded under any of the following conditions: 

(1) Where the system can be grounded so that the maximum 
voltage to ground on the ungrounded conductors does 
not exceed 150 volts 

(2) Where the system is 3-phase, 4-wire, wye connected in 
which the neutral is used as a circuit conductor 

(3) Where the system is 3-phase, 4-wire, delta connected 
in which the midpoint of one phase winding is used as 
a circuit conductor 

(c) Alternating-Current Systems of 1 kV and Over. Alt- 
ernating-current systems supplying mobile or portable 
equipment shall be grounded as specified in Section 250- 
188. Where supplying other than mobile or portable equip- 
ment, such systems shall be permitted to be grounded. Where 
such systems are grounded, they shall comply with the appli- 
cable provisions of this article. 

(d) Separately Derived Systems. If required to be 
grounded as in (a) or (b), separately derived systems shall 
be grounded as specified in Section 250-30. 

FPN No. 1: An alternate ac power source such as an on- 
site generator is not a separately derived system if the neutral 



is solidly interconnected to a service-supplied system neu- 
tral. 

FPN No. 2: For systems that are not separately derived and 
are not required to be grounded as specified in Section 250- 
30, see Section 445-5 for minimum size of conductors that 
must carry fault current. 

250-21. Alternating-Current Systems of 50 Volts to 1000 
Volts Not Required to Be Grounded. The following ac 
systems of 50 volts to 1000 volts shall be permitted to be 
grounded but shall not be required to be grounded: 

(1) Electric systems used exclusively to supply industrial 
electric furnaces for melting, refining, tempering, and 
the like 

(2) Separately derived systems used exclusively for rectifi- 
ers that supply only adjustable speed industrial drives 

(3) Separately derived systems supplied by transformers 
that have a primary voltage rating less than 1000 volts, 
provided that all of the following conditions are met: 

(a) The system is used exclusively for control circuits. 

(b) The conditions of maintenance and supervision en- 
sure that only qualified persons will service the in- 
stallation. 

(c) Continuity of control power is required. 

(d) Ground detectors are installed on the control system. 

(4) Isolated systems as permitted or required in Articles 517 
and 668 

FPN: The proper use of suitable ground detectors on un- 
grounded systems can provide additional protection. 

(5) High-impedance grounded neutral systems as specified 
in Section 250-36 

250-22. Circuits Not to Be Grounded. The following cir- 
cuits shall not be grounded: 

(1) Cranes (circuits for electric cranes operating over com- 
bustible fibers in Class III locations, as provided in 
Section 503-13) 

(2) Health care facilities (circuits as provided in Article 
517) 

(3) Electrolytic cells (circuits as provided in Article 668) 

250-24. Grounding Service-Supplied Alternating-Cur- 
rent Systems. 

(a) System Grounding Connections. A premises wiring 
system that is supplied by an ac service that is grounded 
shall have at each service a grounding electrode conductor 
connected to the grounding electrode(s) required by Part C 
of this article. The grounding electrode conductor shall be 
connected to the grounded service conductor in accordance 
I with (1) through (5). 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-84 



ARTICLE 250 — GROUNDING 



(1) General. The connection shall be made at any acces- 
sible point from the load end of the service drop or service 
lateral to and including the terminal or bus to which the 
grounded service conductor is connected at the service dis- 
connecting means. 

FPN: See definition of Service Drop and Service Lateral in 
Article 100; see also Section 230-21 for overhead supply. 

(2) Outdoor Transformer. Where the transformer sup- 
plying the service is located outside the building, at least 
one additional grounding connection shall be made from the 
grounded service conductor to a grounding electrode, either 
at the transformer or elsewhere outside the building. 

Exception: The additional grounding connection shall not 
be made on high-impedance grounded neutral systems. The 
system shall meet the requirements of Section 250-36. 

(3) Dual Fed Services. For services that are dual fed 
(double ended) in a common enclosure or grouped together 
in separate enclosures and employing a secondary tie, a 
single grounding electrode connection to the tie point of the 
grounded circuit conductors from each power source shall 
be permitted. 

(4) Main Bonding Jumper as Wire or Busbar. Where 
the main bonding jumper specified in Section 250-28 is a 
wire or busbar, and is installed from the neutral bar or bus 
to the equipment grounding terminal bar or bus in the service 
equipment, the grounding electrode conductor shall be per- 
mitted to be connected to the equipment grounding terminal 
bar or bus to which the main bonding jumper is connected. 

(5) Load-Side Grounding Connections. A grounding 
connection shall not be made to any grounded circuit con- 
ductor on the load side of the service disconnecting means' 
except as otherwise permitted in this article. 

FPN: See Section 250-30(b) for separately derived systems, 
Section 250-32 for connections at separate buildings or struc- 
tures, and Section 250-142 for use of the grounded circuit 
conductor for grounding equipment. 

(b) Grounded Conductor Brought to Service Equip- 
ment. Where an ac system operating at less than 1000 volts 
is grounded at any point, the grounded conductor(s) shall 
be run to each service disconnecting means, and shall be 
bonded to each disconnecting means enclosure. The 
grounded conductor(s) shall be installed in accordance with 
(1) through (3). 

Exception: Where more than one service disconnecting 
means is located in an assembly listed for use as service 
equipment, it shall be permitted to run the grounded conduc- 
tors) to the assembly, and the conductor(s) shall be bonded 
to the assembly enclosure. 

(1) Routing. This conductor shall be routed with the 
phase conductors and shall not be smaller than the required 



grounding electrode conductor specified in Table 250-66, but 
shall not be required to be larger than the largest ungrounded 
service-entrance phase conductor. In addition, for service- 
entrance phase conductors larger than 1 100 kcmil copper or 
1750 kcmil aluminum, the grounded conductor shall not be 
smaller than YlVi percent of the area of the largest service- 
entrance phase conductor. 

(2) Parallel Conductors. Where the service-entrance 
phase conductors are installed in parallel, the size of the 
grounded conductor shall be based on the total circular mil 
area of the parallel conductors as indicated in this section. 
Where installed in two or more raceways, the size of the 
grounded conductor in each raceway shall be based on the 
size of the ungrounded service-entrance conductor in the 
raceway but not smaller than No. 1/0. 

FPN: See Section 310-4 for grounded conductors connected 
in parallel. 

(3) High Impedance. The grounded conductor on a 
high-impedance grounded neutral system shall be grounded 
in accordance with Section 250-36. 

(c) Grounding Electrode Conductor. A grounding elec- 
trode conductor shall be used to connect the equipment 
grounding conductors, the service-equipment enclosures, 
and, where the system is grounded, the grounded service 
conductor to the grounding electrode(s) required by Part C 
of this article. 

High-impedance grounded neutral system connections 
shall be made as covered in Section 250-36. 

FPN: See Section 250- 24(a) for ac system grounding con- 
nections. 

(d) Ungrounded System Grounding Connections. A 

premises wiring system that is supplied by an ac service 
that is ungrounded shall have, at each service, a grounding 
electrode conductor connected to the grounding electrode(s) 
required by Part C of this article. The grounding electrode 
conductor shall be connected to a metal enclosure of the 
service conductors at any accessible point from the load 
end of the service drop or service lateral to the service 
disconnecting means. 

250-26. Conductor to Be Grounded — Alternating-Cur- 
rent Systems. For ac premises wiring systems, the conduc- 
tor to be grounded shall be as specified in the following: 

(1) Single-phase, 2- wire — one conductor 

(2) Single-phase, 3-wire — the neutral conductor 

(3) Multiphase systems having one wire common to all 
phases — the common conductor 

(4) Multiphase systems requiring one grounded phase — 
one phase conductor 



1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 250 — GROUNDING 



70-85 



(5) Multiphase systems in which one phase is used as in 
(2) — the neutral conductor 

250-28. Main Bonding Jumper. For a grounded system, 
an unspliced main bonding jumper shall be used to connect 
the equipment grounding conductor(s) and the service-dis- 
connect enclosure to the grounded conductor of the system 
within the enclosure for each service disconnect. 

Exception No. 1: Where more than one service disconnect- 
ing means is located in an assembly listed for use as service 
equipment, an unspliced main bonding jumper shall bond 
the grounded conductor(s) to the assembly enclosure. 

Exception No. 2: Impedance grounded neutral systems shall 
be permitted to be connected as provided in Sections 
250-36 and 250-186. 

(a) Material. Main bonding jumpers shall be of copper or 
other corrosion-resistant material. A main bonding jumper 
shall be a wire, bus, screw, or similar suitable conductor. 

(b) Construction. Whereamainbondingjumperisascrew 
only, the screw shall be identified with a green finish that 
shall be visible with the screw installed. 

(c) Attachment. Main bonding jumpers shall be attached 
in the manner specified by the applicable provisions of Sec- 
tion 250-8. 

(d) Size. The main bonding jumper shall not be smaller 
than the sizes shown in Table 250-66 for grounding electrode 
conductors. Where the service-entrance phase conductors 
are larger than 1 100 kcmil copper or 1750 kcmil aluminum, 
the bonding jumper shall have an area that is not less than 
12 l /2 percent of the area of the largest phase conductor except 
that where the phase conductors and the bonding jumper are 
of different materials (copper or aluminum), the minimum 
size of the bonding jumper shall be based on the assumed 
use of phase conductors of the same material as the bonding 
jumper and with an ampacity equivalent to that of the in- 
stalled phase conductors. 

250-30. Grounding Separately Derived Alternating- 
Current Systems. 

(a) Grounded Systems. A separately derived ac system 
that is grounded shall comply with (1) through (4). 

Exception: High-impedance grounded neutral system 
grounding connection requirements shall not be required to 
comply with (1) and (2) and shall be made as specified in 
Sections 250-36 and 250-186. 

(1) Bonding Jumper. A bonding jumper in compliance 
with Sections 250-28(a) through (d), that is sized for the 
derived phase conductors, shall be used to connect the equip- 



ment grounding conductors of the separately derived system 
to the grounded conductor. Except as permitted by Section 
250-24(a)(4), this connection shall be made at any point on 
the separately derived system from the source to the first 
system disconnecting means or overcurrent device, or it shall 
be made at the source of a separately derived system that 
has no disconnecting means or overcurrent devices. The 
point of connection shall be the same as the grounding 
electrode conductor as required in Section 250-30(a)(2). 

Exception No. 1: A bonding jumper at both the source and 
the first disconnecting means shall be permitted where doing 
so does not establish a parallel path for the grounded circuit 
conductor. Where a grounded conductor is used in this man- 
ner, it shall not be smaller than the size specified for the 
bonding jumper but shall not be required to be larger than the 
ungrounded conductors ). For the purposes of this exception, 
connection through the earth is not considered as providing 
a parallel path. 

Exception No. 2: The size of the bonding jumper for a system 
that supplies a Class 1, Class 2, or Class 3 circuit, and is 
derived from a transformer rated not more than 1000 volt- 
amperes, shall not be smaller than the derived phase con- 
ductors and shall not be smaller than No. 14 copper or No. 
12 aluminum. 

(2) Grounding Electrode Conductor. A grounding 
electrode conductor, sized in accordance with Section 250- 
66 for the derived phase conductors, shall be used to connect 
the grounded conductor of the derived system to the ground- 
ing electrode as specified in (3). Except as permitted by 
Sections 250-24(a)(3) or (a)(4), this connection shall be 
made at the same point on the separately derived system 
where the bonding jumper is installed. 

Exception: A grounding electrode conductor shall not be 
required for a system that supplies a Class 1, Class 2, or 
Class 3 circuit and is derived from, a transformer rated not 
more than 1000 volt-amperes, provided the system grounded 
conductor is bonded to the transformer frame or enclosure 
by a jumper sized in accordance with Section 250-30(a)(l), 
Exception No. 2, and the transformer frame or enclosure is 
grounded by one of the means specified in Section 250-134. 

(3) Grounding Electrode. The grounding electrode 
shall be as near as practicable to and preferably in the same 
area as the grounding electrode conductor connection to the 
system. The grounding electrode shall be the nearest one of 
the following: 

(a) An effectively grounded structural metal member of the 
structure 

(b) An effectively grounded metal water pipe within 5 ft 
(1.52 m) from the point of entrance into the building 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-86 



ARTICLE 250 — GROUNDING 



Exception: In industrial and commercial buildings where 
conditions of maintenance and supervision ensure that only 
qualified persons will service the installation and the entire 
length of the interior metal water pipe that is being used 
for the grounding electrode is exposed, the connection shall 
be permitted at any point on the water pipe system. 

(c) Other electrodes as specified in Sections 250-50 and 
250-52 where the electrodes specified by (a) or (b) are 
not available. 

Exception for (a), (b), and (c): Where a separately derived 
system originates in listed equipment also used as service 
equipment, the grounding electrode used for the service 
equipment shall be permitted as the grounding electrode 
for the separately derived system provided the grounding 
electrode conductor from the service equipment to the 
grounding electrode is of sufficient size for the separately 
derived system. Where the equipment ground bus internal 
to the service equipment is not smaller than the required 
grounding electrode conductor, the grounding electrode con- 
nection for the separately derived system shall be permitted 
to be made to the bus. 

FPN: See Section 250- 104(a)(4) for bonding requirements 
of interior metal water piping in the area served by separately 
derived systems. 

(4) Grounding Methods. In all other respects, ground- 
ing methods shall comply with requirements prescribed in 
other parts of this Code. 

(b) Ungrounded Systems. The equipment of an un- 
grounded separately derived system shall be grounded as 
specified in (1) through (3). 

(1) Grounding Electrode Conductor. A grounding 
electrode conductor, sized in accordance with Section 250^ 
66 for the derived phase conductors, shall be used to connect 
the metal enclosures of the derived system to the grounding 
electrode as specified in" (2). This connection shall be made 
at any point on the separately derived system from the source 
to the first system disconnecting means. 

(2) Grounding Electrode. Except as permitted by Sec- 
tion 250-34 for portable and vehicle mounted generators, the 
grounding electrode shall comply with Section 250-30(a)(3). 

(3) Grounding Methods. In all other respects, ground- 
ing methods shall comply with requirements prescribed in 
other parts of this Code. 

250-32. Two or More Buildings or Structures Supplied 
from a Common Service. 

(a) Grounding Electrode. Where two or more buildings 
or structures are supplied from a common ac service by a 
feeder(s) or branch Circuit(s), the grounding electrode(s) 



required in Part C of this article at each building or structure 
shall be connected in the manner specified in (b) or (c). 
Where there are no existing grounding electrodes, the 
grounding electrode(s) required in Part C of this article shall 
be installed. 

Exception: A grounding electrode at separate buildings or 
structures shall not be required where only one branch cir- 
cuit supplies the building or structure and the branch circuit 
includes an equipment grounding conductor for grounding 
the noncurrent-carrying parts of all equipment. 

(b) Grounded Systems. For a grounded system at the sep- 
arate building or structure, the connection to the grounding 
electrode and grounding or bonding of equipment, structures, 
or frames required to be grounded or bonded shall comply 
with either (1) or (2), 

(1) Equipment Grounding Conductor. An equipment 
grounding conductor as described in Section 250-118 shall 
be run with the supply conductors and connected to the 
building or structure disconnecting means and to the ground- 
ing electrode(s). The equipment grounding conductor shall 
be used for grounding or bonding of equipment, structures, 
or frames required to be grounded or bonded. Any installed 
grounded conductor shall not be connected to the equipment 
grounding conductor or to the grounding electrode(s). 

(2) Grounded Conductor. Where (1) an equipment 
grounding conductor is not run with the supply to the build- 
ing or structure, and (2) there are no continuous metallic 
paths bonded to the grounding system in both buildings 
or structures involved, and (3) ground-fault protection of 
equipment has not been installed on the common ac service, 
the grounded circuit conductor run with the supply to the 
building or structure shall be connected to the building or 
structure disconnecting means and to the grounding elec- 
trode(s) and shall be used for grounding or bonding of equip- 
ment, structures, or frames required to be grounded or 
bonded. 

(c) Ungrounded Systems. The grounding electrode(s) 
shall be connected to the building or structure disconnecting 
means. 

(d) Disconnecting Means Located in Separate Building 
or Structure on the Same Premises. Where one or more 
disconnecting means supply one or more additional build- 
ings or structures under single management, and where these 
disconnecting means are located remote from those buildings 
or structures in accordance with the provisions of Section 
225-32, Exception Nos. 1 and 2, all of the following condi- 
tions shall be met. 



1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 250 — GROUNDING 



70-87 



(1) The connection of the grounded circuit conductor to the 
grounding electrode at a separate building or structure 
shall not be made. 

(2) An equipment grounding conductor for grounding any 
noncurrent-carrying equipment, interior metal piping 
systems, and building or structural metal frames is run 
with the circuit conductors to a separate building or 
structure and bonded to existing grounding electrode(s) 
required in Part C of this article, or, where there are no 
existing electrodes, the grounding electrode(s) required 
in Part C of this article shall be installed where a separate 
building or structure is supplied by more than one branch 
circuit. 

(3) Bonding the equipment grounding conductor to the 
grounding electrode at a separate building or structure 
shall be made in a junction box, panelboard, or similar 
enclosure located immediately inside or outside the sep- 
arate building or structure. 

(e) Agricultural Buildings or Structures. Where live- 
stock is housed, any portion of the equipment grounding 
conductor run underground to the building or structure dis- 
connecting means shall be insulated or covered copper. 

FPN: See Section 547-8 for special grounding requirements 
for agricultural buildings. 

(f) Grounding Conductor. The size of the grounding con- 
ductor to the grounding electrode(s) shall not be less than 
given in Table 250-122, and shall not be required to be 
larger than the largest ungrounded supply conductor. The 
installation shall comply with Part C of this article. 

250-34. Portable and Vehicle-Mounted Generators. 

(a) Portable Generators. The frame of a portable genera- 
tor shall not be required to be grounded and shall be permit- 
ted to serve as the grounding electrode for a system supplied 
by the generator under the following conditions: 

(1) The generator supplies only equipment mounted on the 
generator or cord- and plug-connected equipment 
through receptacles mounted on the generator, or both, 
and 

(2) The noncurrent-carrying metal parts of equipment and 
the equipment grounding conductor terminals of the 
receptacles are bonded to the generator frame. 

(b) Vehicle-Mounted Generators. The frame of a vehicle 
shall be permitted to serve as the grounding electrode for a 
system supplied by a generator located on the vehicle under 
the following conditions: 

(1) The frame of the generator is bonded to the vehicle 
frame, and 



(2) The generator supplies only equipment located on the 
vehicle or cord- and plug-connected equipment through 
receptacles mounted on the vehicle, or both equipment 
located on the vehicle and cord- and plug-connected 
equipment through receptacles mounted on the vehicle 
or on the generator, and 

(3) The noncurrent-carrying metal parts of equipment and 
the equipment grounding conductor terminals of the 
receptacles are bonded to the generator frame, and 

(4) The system complies with all other provisions of this 
article. 

(c) Grounded Conductor Bonding. A system conductor 
that is required to be grounded by Section 250-26 shall be 
bonded to the generator frame where the generator is a 
component of a separately derived system. 

FPN: For grounding portable generators supplying fixed 
wiring systems, see Section 250-20(d). 

250-36. High-Impedance Grounded Neutral Systems. 

High-impedance grounded neutral systems in which a 
grounding impedance, usually a resistor, limits the ground- 
fault current to a low value shall be permitted for 3 -phase 
ac systems of 480 volts to 1000 volts where all of the 
following conditions are met. 

(1) The conditions of maintenance and supervision ensure 
that only qualified persons will service the installation. 

(2) Continuity of power is required. 

(3) Ground detectors are installed on the system. 

(4) Line-to-neutral loads are not served. 

High-impedance grounded neutral systems shall comply 
with the provisions of (a) through (f). 

(a) Grounding Impedance Location. The grounding im- 
pedance shall be installed between the grounding electrode 
conductor and the system neutral. Where a neutral is not 
available, the grounding impedance shall be installed be- 
tween the grounding electrode conductor and the neutral 
derived from a grounding transformer. 

(b) Neutral Conductor. The neutral conductor from the 
neutral point of the transformer or generator to its connection 
point to the grounding impedance shall be fully insulated. 

The neutral conductor shall have an ampacity of not less 
than the maximum current rating of the grounding imped- 
ance. In no case shall the neutral conductor be smaller than 
No. 8 copper or No. 6 aluminum or copper-clad aluminum. 

(c) System Neutral Connection. The system neutral con- 
ductor shall not be connected to ground except through the 
grounding impedance. 

FPN: The impedance is normally selected to limit the 
ground-fault current to a value slightly greater than or equal 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-88 



ARTICLE 250 — GROUNDING 



to the capacitive charging current of the system. This value 
of impedance will also limit transient overvoltages to safe 
values. For guidance, refer to criteria for limiting transient 
overvoltages in Recommended Practice for Grounding of 
Industrial and Commercial Power Systems, ANSI/IEEE 142- 
1991. 

(d) Neutral Conductor Routing. The conductor connect- 
ing the neutral point of the transformer or generator to the 
grounding impedance shall be permitted to be installed in 
a separate raceway. It shall not be required to run this conduc- 
tor with the phase conductors to the first system disconnect- 
ing means or overcurrent device. 

(e) Equipment Bonding Jumper. The equipment bonding 
jumper (the connection between the equipment grounding 
conductors and the grounding impedance) shall be an un- 
spliced conductor run from the first system disconnecting 
means or overcurrent device to the grounded side of the 
grounding impedance. 

(f) Grounding Electrode Conductor Location. The 

grounding electrode conductor shall be attached at any point 
from the grounded side of the grounding impedance to the 
equipment grounding connection at the service equipment 
or first system disconnecting means. 



C. Grounding Electrode System and Grounding 
Electrode Conductor 

250-50. Grounding Electrode System. If available on the 
premises at each building or structure served, each item (a) 
through (d), and any made electrodes in accordance with 
Sections 250-52(c) and (d), shall be bonded together to form 
the grounding electrode system. The bonding jumper(s) shall 
be installed in accordance with Sections 250-64(a), (b), and 
(e), shall be sized in accordance with Section 250-66, and 
shall be connected in the manner specified in Section 250- 
70. , 

An unspliced grounding electrode conductor shall be per- 
mitted to be run to any convenient grounding electrode 
available in the grounding electrode system or to one or 
more grounding electrode(s) individually. It shall be sized for 
the largest grounding electrode conductor required among all 
the electrodes connected to it. 

The grounding electrode conductor shall be unspliced or 
spliced by means of irreversible compression-type connec- 
tors listed for the purpose or by the exothermic welding 
process. 

Interior metal water piping located more than 5 ft (1 .52 m) 
from the point of entrance to the building shall not be used 
as a part of the grounding electrode system or as a conductor 
to interconnect electrodes that are part of the grounding 
electrode system. 



Exception: In industrial and commercial buildings where 
conditions of maintenance and supervision ensure that only 
qualified persons will service the installation and the entire 
length of the interior metal water pipe that is being used 
for the conductor is exposed. 

FPN: See Sections 547-8 and 547-9 for special grounding 
and bonding requirements for agricultural buildings. 

(a) Metal Underground Water Pipe. A metal under- 
ground water pipe in direct contact with the earth for 10 ft 
(3.05 m) or more (including any metal well casing effectively 
bonded to the pipe) and electrically continuous (or made 
electrically continuous by bonding around insulating joints 
or sections or insulating pipe) to the points of connection 
of the grounding electrode conductor and the bonding con- 
ductors. 

(1) Continuity. Continuity of the grounding path or the 
bonding connection to interior piping shall not rely on water 
meters or filtering devices and similar equipment. 

(2) Supplemental Electrode Required. A metal under- 
ground water pipe shall be supplemented by an additional 
electrode of a type specified in Sections 250-50 or 250-52. 
Where the supplemental electrode is a made electrode of 
the rod, pipe, or plate type, it shall comply with Section 
250-56. The supplemental electrode shall be permitted to be 
bonded to the grounding electrode conductor, the grounded 
service-entrance conductor, the nonflexible grounded service 
raceway, or any grounded service enclosure. 

Exception: The supplemental electrode shall be permitted 
to be bonded to the interior metal water piping at any con- 
venient point as covered in Section 250-50, Exception. 

Where the supplemental electrode is a made electrode as 
in Section 250-52(c) or (d), that portion of the bonding 
jumper that is the sole connection to the supplemental 
grounding electrode shall not be required to be larger than 
No. 6 copper wire or No. 4 aluminum wire. 

(b) Metal Frame of the Building or Structure. The metal 
frame of the building or structure, where effectively 
grounded. 

(c) Concrete-Encased Electrode. An electrode encased by 
at least 2 in. (50.8 mm) of concrete, located within and near 
the bottom of a concrete foundation or footing that is in 
direct contact with the earth, consisting of at least 20 ft (6. 1 
m) of one or more bare or zinc galvanized or other electri- 
cally conductive coated steel reinforcing bars or rods of not 
less than '/2-in. (12.7-mm) diameter, or consisting of at least 
20 ft (6.1 m) of bare copper conductor not smaller than 
No. 4. Reinforcing bars shall be permitted to be bonded 
together by the usual steel tie wires or other effective means. 



1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 250 — GROUNDING 



70-89 



(d) Ground Ring. A ground ring encircling the building 
or structure, in direct contact with the earth at a depth below 
the earth's surface of not less than 2Vi ft (762 mm), consisting 
of at least 20 ft (6. 1 m) of bare copper conductor not smaller 
than No. 2. 

250-52. Made and Other Electrodes. Where none of the 
electrodes specified in Section 250-50 is available, one or 
more of the electrodes specified in (b) through (d) shall be 
used. Where practicable, made electrodes shall be embedded 
below permanent moisture level. Made electrodes shall be 
free from nonconductive coatings such as paint or enamel. 
Where more than one electrode is used, each electrode of 
one grounding system (including that used for air terminals) 
shall not be less than 6 ft (1.83 m) from any other electrode 
of another grounding system. Two or more grounding elec- 
trodes that are effectively bonded together shall be consid- 
ered a single grounding electrode system. 

(a) Metal Underground Gas Piping System. A metal un- 
derground gas piping system shall not be used as a grounding 
electrode. 

(b) Other Local Metal Underground Systems or Struc- 
tures. Other local metal underground systems or structures 
such as piping systems and underground tanks. 

(c) Rod and Pipe Electrodes. Rod and pipe electrodes 
shall not be less than 8 ft (2.44 m) in length, shall consist 
of the following materials, and shall be installed in the 
following manner. 

(1) Electrodes of pipe or conduit shall not be smaller 
than 3 /4 in. trade size and, where of iron or steel, shall have 
the outer surface galvanized or otherwise metal-coated for 
corrosion protection. 

(2) Electrodes of rods of iron or steel shall be at least 
5 /s in. (15.87 mm) in diameter. Stainless steel rods less than 
5 /8 in. (15.87 mm) in diameter, nonferrous rods, or their 
equivalent shall be listed and shall not be less than Vi in. 
(12.7 mm) in diameter. 

(3) The electrode shall be installed such that at least 
8 ft (2.44 m) of length is in contact with the soil. It shall 
be driven to a depth of not less than 8 ft (2.44 m) except 
that, Where rock bottom is encountered, the electrode shall 
be driven at an oblique angle not to exceed 45 degrees from 
the vertical or shall be buried in a trench that is at least 
2'/2 ft (762 mm) deep. The upper end of the electrode shall 
be flush with or below ground level unless the aboveground 
end and the grounding electrode conductor attachment are 
protected against physical damage as specified in Section 
250-10. 



(d) Plate Electrodes. Each plate electrode shall expose not 
less than 2 ft 2 (0.186 m 2 ) of surface to exterior soil. Elec- 
trodes of iron or steel plates shall be at least l A in. (6.35 
mm) in thickness. Electrodes of nonferrous metal shall be 
at least 0.06 in. (1.52 mm) in thickness. Plate electrodes 
shall be installed not less than 2 l A ft (762 mm) below the 
surface of the earth. 

(e) Aluminum Electrodes. Aluminum electrodes shall not 
be permitted. 

250-54. Supplementary Grounding Electrodes. Supple- 
mentary grounding electrodes shall be permitted to be con- 
nected to the equipment grounding conductors specified in 
Section 250-1 18, but the earth shall not be used as the sole 
equipment grounding conductor. 

250-56. Resistance of Made Electrodes. A single elec- 
trode consisting of a rod, pipe, or plate that does not have 
a resistance to ground of 25 ohms or less shall be augmented 
by one additional electrode of any of the types specified in 
Sections 250-50 or 250-52. Where multiple rod, pipe, or 
plate electrodes are installed to meet the requirements of 
this section, they shall not be less than 6 ft (1.83 m) apart. 

FPN: The paralleling efficiency of rods longer than 8 ft 
(2.44 m) is improved by spacing greater than 6 ft (1.83 m). 

250-58. Common Grounding Electrode. Where an ac 
system is connected to a grounding electrode in or at a 
building as specified in Sections 250-24 and 250-32, the 
same electrode shall be used to ground conductor enclosures 
and equipment in or on that building. Where separate ser- 
vices supply a building and are required to be connected to 
a grounding electrode, the same grounding electrode shall 
be used. 

Two or more grounding electrodes that are effectively 
bonded together shall be considered as a single grounding 
electrode system in this sense. 

250-60. Use of Air Terminals. Air terminal conductors 
and driven pipes, rods, or other made electrodes used for 
grounding air terminals shall not be used in lieu of the 
made grounding electrodes required by Section 250-52 for 
grounding wiring systems and equipment. This provision 
shall not prohibit the required bonding together of grounding 
electrodes of different systems. 

FPN No. 1 : See Section 250-106 for spacing from air termi- 
nals. See Sections 800-40(d), 810-21 (j), and 820-40(d) for 
bonding of electrodes. 

FPN No. 2: Bonding together of all separate grounding 
electrodes will limit potential differences between them and 
between their associated wiring systems. 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-90 



ARTICLE 250 — GROUNDING 



250-62. Grounding Electrode Conductor Material. The 

grounding electrode conductor shall be of copper, aluminum, 
or copper-clad aluminum. The material selected shall be 
resistant to any corrosive condition existing at the installation 
or shall be suitably protected against corrosion. The conduc- 
tor shall be solid or stranded, insulated, covered, or bare. 

250-64. Grounding Electrode Conductor Installation. 

Grounding electrode conductors shall be installed as speci- 
fied in (a) through (e). 

(a) Aluminum or Copper-Clad Aluminum Conductors. 

Insulated or bare aluminum or copper-clad aluminum 
grounding conductors shall not be used where in direct con- 
tact with masonry or the earth or where subject to corrosive 
conditions. Where used outside, aluminum or copper-clad 
aluminum grounding conductors shall not be installed within 
18 in. (457 mm) of the earth. 

(b) Grounding Electrode Conductor. A grounding elec- 
trode conductor or its enclosure shall be securely fastened 
to the surface on which it is carried. A No. 4 copper or 
aluminum, or larger conductor shall be protected if exposed 
to severe physical damage. A No. 6 grounding conductor 
that is free from exposure to physical damage shall be permit- 
ted to be run along the surface of the building construction 
without metal covering or protection where it is securely 
fastened to the construction; otherwise, it shall be in rigid 
metal conduit, intermediate metal conduit, rigid nonmetallic 
conduit, electrical metallic tubing, or cable armor. Grounding 
conductors smaller than No. 6 shall be in rigid metal conduit, 
intermediate metal conduit, rigid nonmetallic conduit, elec- 
trical metallic tubing, or cable armor. 

(c) Continuous. The grounding electrode conductor shall 
be installed in one continuous length without a splice or 
joint, unless spliced only by irreversible compression-type 
connectors listed for the purpose or by the exothermic weld- 
ing process. 

Exception: Busbars shall be permitted to have splices. 

(d) Grounding Electrode Conductor Taps. Where a ser- 
vice consists of more than a single enclosure as permitted 
in Section 230-40, Exception No. 2, it shall be permitted to 
connect taps to the grounding electrode conductor. Each 
such tap conductor shall extend to the inside of each such 
enclosure. The grounding electrode conductor shall be sized 
in accordance with Section 250-66, but the tap conductors 
shall be permitted to be sized in accordance with the ground- 
ing electrode conductors specified in Section 250-66 for the 
largest conductor serving the respective enclosures. The tap 
conductors shall be connected to the grounding electrode 
conductor in such a manner that the grounding electrode 
conductor remains without a splice or joint. 



(e) Enclosures for Grounding Electrode Conductors. 

Metal enclosures for grounding electrode conductors shall 
be electrically continuous from the point of attachment to 
cabinets or equipment to the grounding electrode, and shall 
be securely fastened to the ground clamp or fitting. Metal 
enclosures that are not physically continuous from cabinet 
or equipment to the grounding electrode shall be made elec- 
trically continuous by bonding each end to the grounding 
conductor. Where a raceway is used as protection for a 
grounding conductor, the installation shall comply with the 
requirements of the appropriate raceway article. 

250-66. Size of Alternating-Current Grounding Elec- 
trode Conductor. The size of the grounding electrode con- 
ductor of a grounded or ungrounded ac system shall not be 
less than given in Table 250-66, except as permitted in (a) 
through (c). 

Table 250-66. Grounding Electrode Conductor for 
Alternating-Current Systems 



Size of Largest Service-Entrance 

Conductor or Equivalent Area 

for Parallel Conductors 1 



Size of Grounding 
Electrode Conductor 



Copper 


Aluminum or 

Copper-Clad 

Aluminum 


Copper 


Aluminum or 

Copper-Clad 

Aluminum 2 


2 or smaller 


Vi or smaller 


8 


6 


1 or 1/0 


2/0 or 3/0 


6 


4 


2/0 or 3/0 


4/0 or 250 
kcmil 


4 


2 


Over 3/0 


Over 250 kcmil 


2 


1/0 


through 350 


through 500 






kcmil 


kcmil 






Over 350 kcmil 


Over 500 kcmil 


1/0 


3/0 


through 600 


through 900 






kcmil 


kcmil 






Over 600 kcmil 


Over 900 kcmil 


2/0 


4/0 


through 1100 


through 1750 






kcmil 


kcmil 






Over 1100 


Over 1750 


3/0 


250 kcmil 


kcmil 


kcmil 







Notes: 

1. Where multiple sets of service-entrance conductors are used as permit- 
ted in Section 230-40, Exception No. 2, the equivalent size of the 
largest service-entrance conductor shall be determined by the largest sum 
of the areas of the corresponding conductors of each set. 

2. Where there are no service-entrance conductors, the grounding elec- 
trode conductor size shall be determined by the equivalent size of the 
largest service-entrance conductor required for the load to be served. 
'This table also applies to the derived conductors of separately derived 
ac systems. 

2 See installation restrictions in Section 250-64(a). 



FPN: See Section 250-24(b) for size of ac system conductor 
brought to service equipment. 



• 



• 



1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 250 — GROUNDING 



70-91 



(a) Connections to Made Electrodes. Where the ground- 
ing electrode conductor is connected to made electrodes as 
permitted in Section 250-52(c) or (d), that portion of the 
conductor that is the sole connection to the grounding elec- 
trode shall not be required to be larger than No. 6 copper 
wire or No. 4 aluminum wire. 

(b) Connections to Concrete-Encased Electrodes. Where 
the grounding electrode conductor is connected to a con- 
crete-encased electrode as permitted in Section 250-50(c), 
that portion of the conductor that is the sole connection to 
the grounding electrode shall not be required to be larger 
than No. 4 copper wire. 

(c) Connections to Ground Rings. Where the grounding 
electrode conductor is connected to a ground ring as permit- 
ted in Section 250-50(d), that portion of the conductor that 
is the sole connection to the grounding electrode shall not 
be required to be larger than the conductor used for the 
ground ring. , 

250-68. Grounding Electrode Conductor Connection to 
Grounding Electrodes. 

(a) Accessibility. The connection of a grounding electrode 
conductor to a grounding electrode shall be accessible. 

Exception: An encased or buried connection to a concrete- 
encased, driven, or buried grounding electrode shall not be 
required to be accessible. 

(b) Effective Grounding Path. The connection of a 
grounding electrode conductor shall be made in a manner 
that will ensure a permanent and effective grounding path. 
Where necessary to ensure the grounding path for a metal 
piping system used as a grounding electrode, effective bond- 
ing shall be provided around insulated joints and sections 
and around any equipment that is likely to be disconnected 
for repairs or replacement. Bonding conductors shall be of 
sufficient length to permit removal of such equipment while 
retaining the integrity of the bond. 

250-70. Methods of Grounding Conductor Connection 
to Electrodes. The grounding conductor shall be connected 
to the grounding electrode by exothermic welding, listed 
lugs, listed pressure connectors, listed clamps, or other listed 
means. Connections depending on solder shall not be used. 
Ground clamps shall be listed for the materials of the ground- 
ing electrode and the grounding electrode conductor and, 
where used on pipe, rod, or other buried electrodes, shall 
also be listed for direct soil burial. Not more than one conduc- 
tor shall be connected to the grounding electrode by a single 
clamp or fitting unless the clamp or fitting is^ listed for 
multiple conductors. One of the following methods shall be 
used: 



(1) A listed bolted clamp of cast bronze or brass, or plain 
or malleable iron 

(2) A pipe fitting, pipe plug, or other approved device 
screwed into a pipe or pipe fitting 

(3) For indoor telecommunications purposes only, a listed 
sheet metal strap-type ground clamp having a rigid metal 
base that seats on the electrode and having a strap of 
such material and dimensions that it is not likely to 
stretch during or after installation 

(4) An equally substantial approved means 



D. Enclosure, Raceway, and Service Cable Grounding 

250-80. Service Raceways and Enclosures. Metal enclo- 
sures and "raceways for service conductors and equipment 
shall be grounded. 

Exception: A metal elbow that is installed in an under- 
ground installation of rigid nonmetallic conduit and is iso- 
lated from possible contact by a minimum cover of 18 in. 
(457 mm) to any part of the elbow shall not be required to 
be grounded. 

250-84. Underground Service Cable or Conduit. 

(a) Underground Service Cable. The sheath or armor of 
a continuous underground metal-sheathed service cable sys- 
tem that is metallically connected to the underground system 
shall not be required to be grounded at the building. The 
sheath or armor shall be permitted to be insulated from the 
interior conduit or piping. 

(b) Underground Service Conduit Containing Cable. 

An underground service conduit that contains a metal- 
sheathed cable bonded to the underground system shall not 
be required to be grounded at the building. The sheath or 
armor shall be permitted to be insulated from the interior 
conduit or piping. 

250-86. Other Conductor Enclosures and Raceways. 

Except as permitted by Section 250-1 12(i), metal enclosures 
and raceways for other than service conductors shall be 
grounded. 

Exception No. 1: Metal enclosures and raceways for con- 
ductors added to existing installations of open wire, knob 
and tube wiring, and nonmetallic- sheathed cable shall not 
be required to be grounded where these enclosures or wiring 
methods 

(a) Do not provide an equipment ground; 

(b) Are in runs of less than 25 ft (7.62 m); 

(c) Are free from probable contact with ground, grounded 
metal, metal lath, or other conductive material; and 

(d) Are guarded against contact by persons. 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-92 



ARTICLE 250 — GROUNDING 



Exception No. 2: Short sections of metal enclosures or race- 
ways used to provide support or protection of cable assem- 
blies from physical damage shall not be required to be 
grounded. 

Exception No. 3: A metal elbow that is installed in an un- 
derground installation of rigid nonmetallic conduit and is 
isolated from possible contact by a minimum cover of 18 
in. (457 mm) to any part of the elbow shall not be required 
to be grounded. 

E. Bonding 

250-90. General. Bonding shall be provided where neces- 
sary to ensure electrical continuity and the capacity to con- 
duct safely any fault current likely to be imposed. 

250-92. Services. 

(a) Bonding of Services. The noncurrent-carrying metal 
parts of equipment indicated in (1), (2), and (3) shall be 
effectively bonded together. 

(1) The service raceways, cable trays, cablebus framework, 
or service cable armor or sheath except as permitted in 
Section 250-84. 

(2) All service enclosures containing service conductors, 
including meter fittings, boxes, or the like, interposed 
in the service raceway or armor. 

(3) Any metallic raceway or armor enclosing a grounding 
electrode conductor as specified in Section 250-64(b). 
Bonding shall apply at each end and to all intervening 
raceways, boxes, and enclosures between the service 
equipment and the grounding electrode. 

(b) Bonding to Other Systems. An accessible means ex- 
ternal to enclosures for connecting intersystem bonding and 
grounding conductors shall be provided at the service by at 
least one of the following means: 

(1) Exposed nonflexible metallic service raceways 

(2) Exposed grounding electrode conductor 

(3) Approved means for the external connection of a copper 
or other corrosion-resistant bonding or grounding con- 
ductor to the service raceway or equipment 

For the purposes of providing an accessible means for 
intersystem bonding, the disconnecting means at a separate 
building or structure as permitted in Section 250-32 and the 
disconnecting means at a mobile home as permitted in Sec- 
tion 550-23(a) shall be considered the service equipment. 

FPN No. 1: A No. 6 copper conductor with one end bonded 
to the service raceway or equipment and with 6 in. (152 
mm) or more of the other end made accessible on the outside 
wall is an example of the approved means covered in (b)(3). 



FPN No. 2: See Sections 800-40, 810-21, and 820-40 for 
bonding and grounding requirements for communications 
circuits, radio and television equipment, and CATV circuits. 

250-94. Method of Bonding at the Service. Electrical 
continuity at service equipment, service raceways, and ser- 
vice conductor enclosures shall be ensured by one of the 
following methods: 

(1) Bonding equipment to the grounded service conductor 
in a manner provided in Section 250-8 

(2) Connections utilizing threaded couplings or threaded 
bosses on enclosures where made up wrenchtight 

(3) Threadless couplings and connectors where made up 
tight for metal raceways and metal-clad cables 

(4) Other approved devices, such as bonding-type locknuts 
and bushings 

Bonding jumpers meeting the other requirements of this 
article shall be used around concentric or eccentric knock- 
outs that are punched or otherwise formed so as to impair 
the electrical connection to ground. Standard locknuts or 
bushings shall not be the sole means for the bonding required 
by this section. 

250-96. Bonding Other Enclosures. 

(a) General. Metal raceways, cable trays, cable armor, 
cable sheath, enclosures, frames, fittings, and other metal 
noncurrent-carrying parts that are to serve as grounding con- 
ductors, with or without the use of supplementary equipment 
grounding conductors, shall be effectively bonded where 
necessary to ensure electrical continuity and the capacity to 
conduct safely any fault current likely to be imposed on 
them. Any nonconductive paint, enamel, or similar coating 
shall be removed at threads, contact points, and contact 
surfaces or be connected by means of fittings designed so 
as to make such removal unnecessary. 

(b) Isolated Grounding Circuits. Where required for the 
reduction of electrical noise (electromagnetic interference) 
on the grounding circuit, an equipment enclosure supplied 
by a branch circuit shall be permitted to be isolated from a 
raceway containing circuits supplying only that equipment 
by one or more listed nonmetallic raceway fittings located 
at the point of attachment of the raceway to the equipment 
enclosure. The metal raceway shall comply with provisions 
of this article and shall be supplemented by an internal 
insulated equipment grounding conductor installed in accor- 
dance with Section 250- 146(d) to ground the equipment 
enclosure. 

FPN: Use of an isolated equipment grounding conductor 
does not relieve the requirement for grounding the raceway 
system. 



• 



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1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 250 — GROUNDING 



70-93 



250-97. Bonding for Over 250 Volts. For circuits of over 
250 volts to ground, the electrical continuity of metal race- 
ways and cables with metal sheaths that contain any conduc- 
tor other than service conductors shall be ensured by one 
or more of the methods specified for services in Sections 
250-94(1) through (4). 

Exception: Where oversized, concentric, or eccentric knock- 
outs are not encountered, or where a box or enclosure with 
concentric or eccentric knockouts is listed for the purpose, 
the following methods shall be permitted: 

(a) Threadless couplings and connectors for cables with 
metal sheaths 

(b) Two locknuts, on rigid metal conduit or intermediate 
metal conduit, one inside and one outside of boxes and 
cabinets 

(c) Fittings with shoulders that seat firmly against the box 
or cabinet, such as electrical metallic tubing connectors, 
flexible metal conduit connectors, and cable connectors, 
with one locknut on the inside of boxes and cabinets 

(d) Listed fittings 

250-98. Bonding Loosely Jointed Metal Raceways. Ex- 
pansion fittings and telescoping sections of metal raceways 
shall be made electrically continuous by equipment bonding 
jumpers or other means. 

250-100. Bonding in Hazardous (Classified) Loca- 
tions. Regardless of the voltage of the electrical system, the 
electrical continuity of noncurrent-carrying metal parts of 
equipment, raceways, and other enclosures in any hazardous 
(classified) location as defined in Article 500 shall be en- 
sured by any of the methods specified for services in Section 
250-94 that are approved for the wiring method used. 

250-102. Equipment Bonding Jumpers. 

(a) Material. Equipment bonding jumpers shall be of cop- 
per or other corrosion-resistant material. A bonding juniper 
shall be a wire, bus, screw, or similar suitable conductor. 

(b) Attachment. Equipment bonding jumpers shall be 
attached in the manner specified by the applicable provisions 
of Section 250-8 for circuits and equipment and by Section 
250-70 for grounding electrodes. 

(c) Size — Equipment Bonding Jumper on Supply Side 
of Service. The bonding jumper shall not be smaller-man 
the sizes shown in Table 250-66 for grounding electrode 
conductors. Where the service-entrance phase conductors 
are larger than 1 100 kcmil copper or 1750 kcmil aluminum, 
the bonding jumper shall have an area not less than 12!/2 
percent of the area of the largest phase conductor except 
that, where the phase conductors and the bonding jumper 
are of different materials (copper or aluminum), the mini- 



mum size of the bonding jumper shall be based on the 
assumed use of phase conductors of the same material as 
the bonding jumper and with an ampacity equivalent to that 
of the installed phase conductors. Where the service-entrance 
conductors are paralleled in two or more raceways or cables, 
the equipment bonding jumper, where routed with the race- 
ways or cables, shall be run in parallel. The size of the 
bonding jumper for each raceway or cable shall be based 
on the size of the service-entrance conductors in each race- 
way or cable. 

The bonding jumper for a grounding electrode conductor 
raceway or cable armor as covered in Section 250-64(d) 
shall be the same size or larger than the required enclosed 
grounding electrode conductor. 

(d) Size — Equipment Bonding Jumper on Load Side 
of Service. The equipment bonding jumper on the load 
side of the service overcurrent devices shall be sized, as a 
minimum, in accordance with the sizes listed in Table 250- 
122, but not required to be larger than the circuit conductors 
supplying the equipment, and not smaller than No. 14. 

A single common continuous equipment bonding jumper 
shall be permitted to bond two or more raceways or cables 
where the bonding jumper is sized in accordance with Table 
250-122 for the largest overcurrent device supplying circuits 
therein. 

(e) Installation. The equipment bonding jumper shall be 
permitted to be installed inside or outside of a raceway or 
enclosure. Where installed on the outside, the length of the 
equipment bonding jumper shall not exceed 6 ft (1.83 m) 
and shall be routed with the raceway or enclosure. Where 
installed inside of a raceway, the equipment bonding jumper 
shall comply with the requirements of Sections 250-1 19 and 
250-148. 

250-104. Bonding of Piping Systems and Exposed Struc- 
tural Steel. 

(a) Metal Water Piping. The interior metal water piping 
system shall be bonded as required in (1), (2), (3), or (4) 
of this section. The bonding jumper shall be installed in 
accordance with Section 250-64(a), (b), and (e). The points 
of attachment of the bonding jumper(s) shall be accessible. 

(1) General. The interior metal water piping system 
shall be bonded to the service equipment enclosure, the 
grounded conductor at the service, the grounding electrode 
conductor where of sufficient size, or to the one or more 
grounding electrodes used. The bonding jumper shall be 
sized in accordance with Table 250-66 except as permitted 
in (2) and (3). 

(2) Buildings of Multiple Occupancy. In buildings of 
multiple occupancy, where the interior metal water piping 
system for the individual occupancies is metallically isolated 



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ARTICLE 250 — GROUNDING 



from all other occupancies by use of nonmetallic water pip- 
ing, the interior metal. water piping system for each occu- 
pancy shall be permitted to be bonded to the equipment 
grounding terminal of the panelboard or switchboard enclo- 
sure (other than service equipment) supplying that occu- 
pancy. The bonding jumper shall be sized in accordance 
with Table 250-122. 

(3) Multiple Buildings or Structures Supplied from a 
Common Service. The interior metal water piping system 
shall be bonded to the building or structure disconnecting 
means enclosure where located at the building or structure, 
or to the equipment grounding conductor run with the supply 
conductors, or to the one or more grounding electrodes used. 
The bonding jumper shall be sized in accordance with Sec- 
tion 250-122 based on the rating or setting of the largest 
overcurfent device protecting the feeder(s) or branch cir- 
cuit(s) that supply the building. 

(4) Separately Derived Systems. The grounded con- 
ductor of the separately derived system shall be bonded to 
the nearest available point of the interior metal water piping 
system in the area served by the separately derived system. 
This connection shall be made at the same point on the 
separately derived system where the grounding electrode 
conductor is connected. The bonding jumper shall be sized 
in accordance with Table 250-66. 

x (b) Metal Gas Piping. Each aboveground portion of a gas 
piping system upstream from the equipment shutoff valve 
shall be electrically continuous and bonded to the grounding 
electrode system. 

(c) Other Metal Piping. Interior metal piping that may 
become energized shall be bonded to the service equipment 
enclosure, the grounded conductor at the service, the ground- 
ing electrode conductor where of sufficient size, or to the 
one or more grounding electrodes used. The bonding jumper 
shall be sized in accordance with Table 250-122 using the 
rating of the circuit that may energize the piping. 

The equipment grounding conductor for the circuit that 
may energize the piping shall be permitted to serve as the 
bonding means. 

FPN: Bonding all piping and metal air ducts within the 
premises will provide additional safety. 

(d) Structural Steel. Exposed interior structural steel that 
is interconnected to form a steel building frame and is not 
intentionally grounded and may become energized shall be 
bonded to the service equipment enclosure, the grounded 
conductor at the service, the grounding electrode conductor 
where of sufficient size, or to the one or more grounding 
electrodes used. The bonding jumper shall be sized in accor- 
dance with Table 250-66 and installed in accordance, with 



Sections 250-64(a), (b), and (e). The points of attachment 
of the bonding jumpers shall be accessible. 

250-106. Lightning Protection Systems. The lightning 
protection system ground terminals shall be bonded to the 
building or structure grounding electrode system. 

FPN No. 1: See Section 250-60 for use of air terminals. 
For further information, see Standard for the Installation 
of Lightning Protection Systems, NFPA 780-1997,. which 
contains detailed information on grounding, bonding, and 
spacing from lightning protection systems. 

FPN No. 2: Metal raceways, enclosures, frames, and other 
noncurrent-carrying metal parts of electric equipment in- 
stalled on a building equipped with a lightning protection 
system may require bonding or spacing from the lightning 
protection conductors in accordance with Standard for the 
Installation of Lightning Protection Systems, NFPA 780- 
1997. Separation from lightning protection conductors is 
typically 6 ft (1.83 m) through air or 3 ft (0.92 m) through 
dense materials such as concrete, brick, or wood. 



F. Equipment Grounding and Equipment Grounding 
Conductors 

250-110. Equipment Fastened in Place or Connected by 
Permanent Wiring Methods (Fixed). Exposed noncur- 
rent-carrying metal parts of fixed equipment likely to be- 
come energized shall be grounded under any of the following 
conditions: 

(1) Where within 8 ft (2.44 m) vertically or 5 ft (1.52 m) 
horizontally of ground or grounded metal objects and 
subject to contact by persons 

(2) Where located in a wet or damp location and not isolated 

(3) Where in electrical contact with metal 

(4) Where in a hazardous (classified) location as covered 
by Articles 500 through 517 

(5) Where supplied by a metal-clad, metal-sheathed, metal- 
raceway, or other wiring method that provides an equip- 
ment ground, except as permitted by Section 250-86, 
Exception No. 2 for short sections of metal enclosures 

(6) Where equipment operates with any terminal at over 
150 volts to ground 

Exception No. 1 to (1) through (6): Metal frames of electri- 
cally heated appliances, exempted by special permission, in 
which case the frames shall be permanently and effectively 
insulated from ground. 

Exception No. 2 to (1) through (6): Distribution apparatus, 
such as transformer and capacitor cases, mounted on 
wooden poles, at a height exceeding 8 ft (2.44 m) above 
ground or grade level. 

Exception No. 3 to (1) through (6): Listed equipment pro- 
tected by a system of double insulation, or its equivalent, 



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shall not be required to be grounded. Where such a system 
is employed, the equipment shall be distinctively marked. 

250-112. Fastened in Place or Connected by Permanent 
Wiring Methods (Fixed) — Specific. Exposed, noncur- 
rent-carrying metal parts of the kinds of equipment described 
in (a) through (k), and noncurrent-carrying metal parts of 
equipment and enclosures described in (1) and (m), shall be 
grounded regardless of voltage. 

(a) Switchboard Frames and Structures. Switchboard 
frames and structures supporting switching equipment, ex- 
cept frames of 2-wire dc switchboards where effectively 
insulated from ground. 

(b) Pipe Organs. Generator and motor frames in an elec- 
trically operated pipe organ, unless effectively insulated from 
ground and the motor driving it. 

(c) Motor Frames. Motor frames, as provided by Section 
430-142. 

(d) Enclosures for Motor Controllers. Enclosures for 
motor controllers unless attached to ungrounded portable 
equipment. 

(e) Elevators arid Cranes. Electric equipment for eleva- 
tors and cranes. 

(f) Garages, Theaters, and Motion Picture Studios. El- 
ectric equipment in commercial garages, theaters, and mo- 
tion picture studios, except pendant lampholders supplied 
by circuits not over 150 volts to ground. * 

(g) Electric Signs. Electric signs, outline lighting, and as- 
sociated equipment as provided in Article 600. 

(h) Motion Picture Projection Equipment. Motion pic- 
ture projection equipment. 

(i) Power-Limited Remote-Control, Signaling, and Fire 
Alarm Circuits. Equipment supplied by Class 1 power- 
limited circuits and Class 1, Class 2, and Class 3 remote- 
control and signaling circuits, and by fire alarm circuits, 
shall be grounded where system grounding is required by 
Part B of this article. 

(j) Lighting Fixtures. Lighting fixtures as provided in Part 
E of Article 410. 

(k) Skid-Mounted Equipment. Permanently mounted 
electrical equipment and skids shall be grounded with an 
equipment bonding jumper sized as required by Section 
250-122. 

(1) Motor-Operated Water Pumps. Motor-operated water 
pumps including the submersible type. 



(m) Metal Well Casings. Where a submersible pump is 
used in a metal well casing, the well casing shall be bonded 
to the pump circuit equipment grounding conductor. 

250-114. Equipment Connected by Cord and Plug. 

Under any of the conditions described in (1) through (4), 
exposed noncurrent-carrying metal parts of cord- and plug- 
connected equipment likely to become energized shall be 
grounded. 

Exception: Listed tools, listed appliances, and listed equip- 
ment covered in (2) through (4) shall not be required to be 
grounded where protected by a system of double insuldtion 
or its equivalent. Double insulated equipment shall be dis- 
tinctively marked. 

(1) In hazardous (classified) locations (see Articles 500 
through 517) 

(2) Where operated at over 150 volts to ground 

Exception No. 1: Motors, where guarded, shall not be re- 
quired to be grounded. 

Exception No. 2: Metal frames of electrically heated appli- 
ances, exempted by special permission, shall not be required 
to be grounded, in which case the frames shall be perma- 
nently and effectively insulated from ground. 

(3) In residential occupancies 

(a) Refrigerators, freezers, and air conditioners 

(b) Clothes-washing, clothes-drying, dish-washing ma- 
chines; information technology equipment; sump 
pumps and electrical aquarium equipment 

(c) Hand-held motor-operated tools, stationary and 
fixed motor-operated tools, light industrial motor- 
operated tools 

(d) Motor-operated appliances of the following types: 
hedge clippers, lawn mowers, snow blowers, and 
wet scrubbers 

(e) Portable handlamps 

(4) In other than residential occupancies 

(a) Refrigerators, freezers, and air conditioners 

(b) Clothes-washing, clothes-drying, dish-washing ma- 
chines; information technology equipment; sump 
pumps and electrical aquarium equipment 

(c) Hand-held motor-operated tools, stationary and 
fixed motor-operated tools, light industrial motor- 
operated tools 

(d) Motor-operated appliances of the following types: 
hedge clippers, lawn mowers, snow blowers, and 
wet scrubbers 

(e) Cord- and plug-connected appliances used in damp 
or wet locations or by persons standing on the 



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ARTICLE 250 — GROUNDING 



ground or on metal floors or working inside of metal 
tanks or boilers 

(f) Tools likely to be used in wet or conductive locations 

(g) Portable handlamps 

Exception: Tools and portable handlamps likely to be used 
in wet or conductive locations shall not be required to be 
grounded where supplied through an isolating transformer 
with an ungrounded secondary of not over 50 volts. 

250-116. Nonelectric Equipment. The metal parts of non- 
electric equipment described in this section shall be 
grounded. 

(1) Frames and tracks of electrically operated cranes and 
hoists 

(2) Frames of nonelectrically driven elevator cars to which 
electric conductors are attached 

(3) Hand-operated metal shifting ropes or cables of electric 
elevators 

FPN: Where extensive metal in or on buildings may become 
energized and is subject to personal contact, adequate bond- 
ing and grounding will provide additional safety. 

250-118. Types of Equipment Grounding Conductors. 

The equipment grounding conductor run with or enclosing 
the circuit conductors shall be one or more or a combination 
of the following. 

(1) A copper or other corrosion-resistant conductor. This 
conductor shall be solid or stranded; insulated, covered, 
or bare; and in the form of a wire or a busbar of any 
shape. 

(2) Rigid metal conduit. 

(3) Intermediate metal conduit. 

(4) Electrical metallic tubing. 

(5) Flexible metal conduit where both the conduit and 
fittings are listed for grounding. 

(6) Listed flexible metal conduit that is not listed for 
grounding, meeting all the following conditions. 

(a) The conduit is terminated in fittings listed for 
grounding. 

(b) The circuit conductors contained in the conduit 
are protected by overcurrent devices rated at 20 
amperes or less. 

(c) The combined length of flexible metal conduit and 
flexible metallic tubing and liquidtight flexible 
metal conduit in the same ground return path does 
not exceed 6 ft (1.83 m). 

(d) The conduit is not installed for flexibility. 

(7) Listed liquidight flexible metal conduit meeting all the 
following conditions. 



(a) The conduit is terminated in fittings listed for 
grounding. 

(b) For trade sizes 3 /s in. through Vi in., the circuit 
conductors contained in the conduit are protected 
by overcurrent devices rated at 20 amperes or less. 

(c) For trade sizes 3 A in. through VA in., the circuit 
conductors contained in the conduit are protected 
by overcurrent devices rated not more than 60 am- 
peres and there is no flexible metal conduit, flexible 
metallic tubing, or liquidtight flexible metal con- 
duit in trade sizes 3 /s in. or Vi in. in the grounding 
path. 

(d) The combined length of flexible metal conduit and 
flexible metallic tubing and liquidtight flexible 
metal conduit in the same ground return path does 
not exceed 6 ft (1.83 m). 

(e) The conduit is not installed for flexibility. 

(8) Flexible metallic tubing where the tubing is terminated 
in fittings listed for grounding and meeting all the 
following conditions. 

(a) The circuit conductors contained in the tubing are 
protected by overcurrent devices rated at 20 am- 
peres or less. 

(b) The combined length of flexible metal conduit and 
flexible metallic tubing and liquidtight flexible 
metal conduit in the same ground return path does 
not exceed 6 ft (1.83 m). 

(9) Armor of Type AC cable as provided in Section 333-21. 

(10) The copper sheath of mineral-insulated, metal-sheathed 
cable. 

(11) The metallic sheath or the combined metallic sheath and 
grounding conductors of Type MC cable. ■ 

(12) Cable trays as permitted in Sections 318-3(c) and 
318-7. 

(13) Cablebus framework as permitted in Section 365-2(a). 

(14) Other electrically continuous metal raceways listed for 
grounding. 

250-119. Identification of Equipment Grounding Con- 
ductors. Unless required elsewhere in this Code, equipment 
grounding conductors shall be permitted to be bare, covered, 
or insulated. Individually covered or insulated equipment 
grounding conductors shall have a continuous outer finish 
that is either green or green with one or more yellow stripes 
except as permitted in this section. 

(a) Conductors Larger than No. 6. An insulated or cov- 
ered conductor larger than No. 6 copper or aluminum shall 
be permitted, at the time of installation, to be permanently 
identified as an equipment grounding conductor at each end 
and at every point where the conductor is accessible. Identi- 
fication shall be accomplished by one of the following: 



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(1) Stripping the insulation or covering from the entire ex- 
posed length 

(2) Coloring the exposed insulation or covering green 

(3) Marking the exposed insulation or covering with green 
tape or green adhesive labels 

(b) Multiconductor Cable. Where the conditions of main- 
tenance and supervision ensure that only qualified persons 
will service the installation, one or more insulated conductors 
in a multiconductor cable, at the time of installation, shall 
be permitted to be permanently identified as equipment 
grounding conductors at each end and at every point where 
the conductors are accessible by one of the following means: 

(1) Stripping the insulation from the entire exposed length 

(2) Coloring the exposed insulation green 

(3) Marking the exposed insulation with green tape or green 
adhesive labels 

(c) Flexible Cord. An uninsulated equipment grounding 
conductor shall be permitted, but, if individually covered, 
the covering shall have a continuous outer finish that is 
either green or green with one or more yellow stripes. 

250-120. Equipment Grounding Conductor Installa- 
tion. An equipment grounding conductor shall be installed 
as follows. 

(a) Raceway, Cable Trays, Cable Armor, or Cable 
Sheaths. Where it consists of a raceway, cable tray, cable 
armor, or cable sheath or where it is a wire within a raceway 
or cable, it shall be installed in accordance with the applica- 
ble provisions in this Code using fittings for joints and 
terminations approved for use with the type raceway or cable 
used. All connections, joints, and fittings shall be made tight 
using suitable tools. 

(b) Aluminum and Copper-Clad Aluminum Conduc- 
tors. Aluminum and copper-clad aluminum conductors 
shall be installed in accordance with the restrictions of Sec- 
tion 250-64. 

(c) Equipment Grounding Conductors Smaller than 

No. 6. Equipment grounding conductors smaller than No. 
6 shall be protected from physical damage by a raceway or 
cable armor except where run in hollow spaces of walls or 
partitions, where not subject to physical damage, or where 
protected from physical damage. 

250-122. Size of Equipment Grounding Conductors. 

(a) General. Copper, aluminum, or copper-clad aluminum 
equipment grounding conductors of the wire type shall not 
be smaller than shown in Table 250-122, but shall not be 
required to be larger than the circuit conductors supplying 



the equipment. Where a raceway or a cable armor or sheath 
is used as the equipment grounding conductor, as provided 
in Sections 250-118 and 250- 134(a), it shall comply with 
Section 250-2(d). 

(b) Adjustment for Voltage Drop. Where conductors are 
adjusted in size to compensate for voltage drop, equipment 
grounding conductors, where installed, shall be adjusted pro- 
portionately according to circular mil area. 

(c) Multiple Circuits. Where a single equipment ground- 
ing conductor is run with multiple circuits in the same race- 
'way or cable, it shall be sized for the largest overcurrent 
device protecting conductors in the raceway or cable. 

(d) Motor Circuits. Where the overcurrent device consists 
of an instantaneous trip circuit breaker or a motor short- 
circuit protector, as allowed in Section 430-52, the equip- 
ment grounding conductor size shall be permitted to be based 
on the rating of the motor overload protective device but 
not less than the size shown in Table 250-122. 

(e) Flexible Cord and Fixture Wire. Equipment ground- 
ing conductors that are part of flexible cords or used with 
fixture wires in accordance with Section 240-4 shall be not 
smaller than No. 18 copper and not smaller than the circuit 
conductors. 

(f) Conductors in Parallel. Where conductors are run in 
parallel in multiple raceways or cables as permitted in Sec- 
tion 310-4, the equipment grounding conductors, where 
used, shall be run in parallel in each raceway or cable. 
One of the following methods shall be used to ensure the 
equipment grounding conductors are protected. 

(1) Each parallel equipment grounding conductor shall 
be sized on the basis of the ampere rating of the overcurrent 
device protecting the circuit conductors in the raceway or 
cable in accordance with Table 250-122. 

(2) Where ground-fault protection of equipment is in- 
stalled, each parallel equipment grounding conductor in a 
multiconductor cable shall be permitted to be sized in accor- 
dance with Table 250-122 on the basis of the trip rating of 
the ground-fault protection where the following conditions 
are met. 



(1) Conditions of maintenance and supervision ensure that 
only qualified persons will service the installation. 

(2) The ground-fault protection equipment is set to trip at 
not more than the ampacity of a single ungrounded 
conductor of one of the cables in parallel. 

(3) The ground-fault protection is listed for the purpose. 



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ARTICLE 250 — GROUNDING 



Table 250-122. Minimum Size Equipment Grounding 
Conductors for Grounding Raceway and Equipment 



Rating or Setting of 
Automatic Overcurrent 


(AWG 


Size 
or kcmil) 


Device in Circuit Ahead 

of Equipment, Conduit, 

etc., Not Exceeding 

(Amperes) 


Copper 


Aluminum or 
Copper-Clad 
Aluminum* 


15 


14 


12 


20 


12 


10 


30 


10 


8 


40 


10 


8 


60 


10 


8 


100 


8 


6 


200 


6 


4 


300 


4 


2 


400 . 


3 


1 


500 


2 


1/0 


600 


1 


2/0 


800 


1/0 


3/0 


1000 


2/0 


4/0 


1200 


3/0 


250 


1600 


4/0 


350 


2000 


250 


400 


2500 


350 


600 


3000 


400 


600 


4000 


500 


800 


5000 


700 


1200 


6000 


800 


1200 



Note: Where necessary to comply with Section 250-2(d), the equipment 
grounding conductor shall be sized larger than this table. 
*See installation restrictions in Section 250-120. 



250-124. Equipment Grounding Conductor Continuity. 

(a) Separable Connections. Separable connections such 
as those provided in drawout equipment or attachment plugs 
and mating • connectors and receptacles shall provide for 
first-make, last-break of the equipment grounding conductor. 
First-make, last-break shall not be required where inter- 
locked equipment, plugs, receptacles, and connectors pre- 
clude energization without grounding continuity. 

(b) Switches. No automatic cutout or switch shall be placed 
in the equipment grounding conductor of a premises wiring 
system unless the opening of the cutout or switch disconnects 
all sources of energy. 

250-126. Identification of Wiring Device Terminals. The 

terminal for the connection of the equipment grounding con- 
ductor shall be identified by one of the following. 

(1) A green, not readily removable terminal screw with a 
hexagonal head. 



(2) A green, hexagonal, not readily removable terminal nut. 

(3) A green pressure wire connector. If the terminal for 
the grounding conductor is not visible, the conductor 
entrance hole shall be marked with the word green or 
ground, the letters G or GR or the grounding symbol 
shown in Figure 250- 126, -or otherwise identified by a 
distinctive green color. If the terminal for the equipment 
grounding conductor is readily removable, the area adja- 
cent to the terminal shall be similarly marked. 



Figure 250-126 Grounding symbol. 



G. Methods of Equipment Grounding 

250-130. Equipment Grounding Conductor Connec- 
tions. Equipment grounding conductor connections at the 
source of separately derived systems shall be made in accor- 
dance with Section 250-30(a)(l). Equipment grounding con- 
ductor connections at service equipment shall be made as 
indicated in (a) or (b). For replacement of nongrounding- 
type receptacles with grounding type receptacles and for 
branch-circuit extensions only in existing" installations that 
do not have an equipment grounding conductor in the branch 
circuit, connections shall be permitted as indicated in (c). 

(a) For Grounded Systems. The connection shall be made 
by bonding the equipment grounding conductor to the 
grounded service conductor and the grounding electrode 
conductor. 

(b) For Ungrounded Systems. The connection shall be 
made by bonding the equipment grounding conductor to the 
grounding electrode conductor. 

(c) Nongrounding Receptacle Replacement or Branch 
Circuit Extensions. The equipment grounding conductor 
of a grounding-type receptacle or a branch-circuit extension 
shall be permitted to be connected to any of the following: 

(1) Any accessible point on the grounding electrode system 
as described in Section 250-50 

(2) Any accessible point on the grounding electrode con- 
ductor 

(3) The equipment grounding terminal bar within the enclo- 
sure where the branch circuit for the receptacle or branch 
circuit originates 

(4) For grounded systems, the grounded service conductor 
within the service equipment enclosure 

(5) For ungrounded systems, the grounding terminal bar 
within the service equipment enclosure 

FPN: See Section 210-7(d) for the use of a ground-fault 
I circuit-interrupting type of receptacle. 



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70-99 



250-132. Short Sections of Raceway. Isolated sections of 
metal raceway or cable armor, where required to be 
grounded, shall be grounded in accordance with Section 
250-134. 

250-134. Equipment Fastened in Place or Connected by 
Permanent Wiring Methods (Fixed) — Grounding. Un- 
less grounded by connection to the grounded circuit conduc- 
tor as permitted by Sections 250-32, 250-140, and 250-142, 
noncurrent-carrying metal parts of equipment, raceways, and 
other enclosures, if grounded, shall be grounded by one of 
the following methods. 

(a) Equipment Grounding Conductor Types. By any of 

the equipment grounding conductors permitted by Section 
250-118. 

(b) With Circuit Conductors. By an equipment grounding 
conductor contained within the same raceway, cable, or 
otherwise run with the circuit conductors. 

Exception No. 1: As provided in Section 250-130(c), the 
equipment grounding conductor shall be permitted to be run 
separately from the circuit conductors. 

Exception No. 2: For dc circuits, -the. equipment grounding 
conductor shall be permitted to be run separately from the 
circuit conductors. 

FPN No. 1: See Sections 250-102 and 250-168 for equip- 
ment bonding jumper requirements. 



FPN No. 2: 
equipment. 



See Section 400-7 for use of cords for fixed 



250-136. Equipment Considered Effectively Grounded. 

Under the conditions specified in (a) and (b), the noncurrent- 
carrying metal parts of the equipment shall be considered 
effectively grounded. 

(a) Equipment Secured to Grounded Metal Supports. 

Electric equipment secured to and in electrical contact with 
a metal rack or structure provided for its support and 
grounded by one of the means indicated in Section 250-134. 
The structural metal frame of a building shall not be used 
as the required equipment grounding conductor for ac equip- 
ment. 

(b) Metal Car Frames. Metal car frames supported by 
metal hoisting cables attached to or running over metal 
sheaves or drums of elevator machines that are grounded 
by one of the methods indicated in Section 250-134. .;;.- 

250-138. Cord- and Plug-Connected Equipment. Non- 
current-carrying metal parts of cord- and plug-connected 
equipment if grounded, shall be grounded by one of the 
following methods. 



(a) By Means of an Equipment Grounding Conductor. 

By means of an equipment grounding conductor run with 
the power supply conductors in a cable assembly or flexible 
cord properly terminated in a grounding-type attachment 
plug with one fixed grounding contact. 

Exception: The grounding contacting pole of grounding- 
type plug-in ground-fault circuit interrupters shall be per- 
mitted to be of the movable, self-restoring type on circuits 
operating at not over 150 volts between any two conductors, 
or over 150 volts between any conductor and ground. 

(b) By Means of a Separate Flexible Wire or Strap. By 

means of a separate flexible wire or strap, insulated or bare, 
protected as well as practicable against physical damage, 
where part of equipment. 

250-140. Frames of Ranges and Clothes Dryers. This 
section shall apply to existing branch-circuit installations 
only. New branch-circuit installations shall comply with Sec- 
tions 250-134 and 250-138. Frames of electric ranges, wall- 
mounted ovens, counter-mounted cooking units, clothes dry- 
ers, and outlet or junction boxes that are part of the circuit 
for these appliances shall be grounded in the manner speci- 
fied by Section 250-134 or 250-138; or, except for mobile 
homes and recreational vehicles, shall be permitted to be 
grounded to the grounded circuit conductor if all of the 
following conditions are met. 

(1) The supply circuit is 120/240- volt, single-phase, 3-wire; 
or 208 Y/ 120- volt derived from a 3 -phase, 4- wire wye- 
connected system. 

(2) The grounded conductor is not smaller than No. 10 
copper or No. 8 aluminum. 

(3) The grounded conductor is insulated, or the grounded 
conductor is uninsulated and part of a Type SE service- 
entrance cable and the branch circuit originates at the 
service equipment. 

(4) Grounding contacts of receptacles furnished as part of 
the equipment are bonded to the equipment. 

250-142. Use of Grounded Circuit Conductor for 
Grounding Equipment. 

(a) Supply-Side Equipment. A grounded circuit conduc- 
tor shall be permitted to ground noncurrent-carrying metal 
parts of equipment, raceways, and other enclosures at any 
of the following locations: 

(1) On the supply side or within the enclosure of the ac 
service-disconnecting means 

(2) On the supply side or within the enclosure of the main 
disconnecting means for separate buildings as provided 
in Section 250-32(b) 



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ARTICLE 250 — GROUNDING 



(3) On the supply side or within the enclosure of the main 
disconnecting means or overcurrent devices of a sepa- 
rately derived system where permitted by Section 250- 
30(a)(1) 

(b) Load-Side Equipment. Except as permitted in Sec- 
tions 250-30(a)(l) and 250-32(b), a grounded circuit con- 
ductor shall not be used for grounding noncurrent-carrying 
metal parts of equipment on the load side of the service 
disconnecting means or on the load side of a separately 
derived system disconnecting means or the overcurrent de- 
vices for a separately derived system not having a main 
disconnecting means. 

Exception No. 1: The frames of ranges, wall-mounted ovens, 
counter-mounted cooking units, and clothes dryers under 
the conditions permitted for existing installations by Section 
250-140 shall be permitted to be grounded by a grounded 
circuit conductor. 

Exception No. 2: It shall be permissible to ground meter 
enclosures by connection to the grounded circuit conductor 
on the load-side of the service disconnect if 

(a) No service ground-fault protection is installed, and 

(b) All meter enclosures are located near the service discon- 
necting means, and 

(c) The size of the grounded circuit conductor is not smaller 
than the size specified in Table 250-122 for equipment 
grounding conductors. 

Exception No. 3: Direct-current systems shall be permitted 
to be grounded on the load side of the disconnecting means 
or overcurrent device in accordance with Section 250-164. 

250-144. Multiple Circuit Connections. Where equip- 
ment is required to be grounded, and is supplied by separate 
connection to more than one circuit or grounded premises 
wiring system, a means for grounding shall be provided for 
each such connection as specified in Sections 250-134 and 
250-138. 

250-146. Connecting Receptacle Grounding Terminal to 

Box. An equipment bonding jumper shall be used to connect 
the grounding terminal of a grounding-type receptacle to a 
grounded box unless grounded as in (a) through (d). 

(a) Surface Mounted Box. Where the box is mounted on 
or at the surface, direct metal-to-metal contact between the 
device yoke and the box shall be permitted to ground the 
receptacle to the box. This provision shall not apply to cover- 
mounted receptacles unless the box and cover combination 
are listed as providing satisfactory ground continuity be- 
tween the box and the receptacle. 

(b) Contact Devices or Yokes. Contact devices or yokes 
designed and listed for the purpose shall be permitted in 



conjunction with the supporting screws to establish the 
grounding circuit between the device yoke and flush-type 
boxes. 

(c) Floor Boxes. Floor boxes designed for and listed as 
providing satisfactory ground continuity between the box 
and the device shall be permitted. 

(d) Isolated Receptacles. Where required for the reduction 
of electrical noise (electromagnetic interference) on the 
grounding circuit, a receptacle in which the grounding termi- 
nal is purposely insulated from the receptacle mounting 
means shall be permitted. The receptacle grounding terminal 
shall be grounded by an insulated equipment grounding 
conductor run with the circuit conductors. This grounding 
conductor shall be permitted to pass through one or more 
panelboards without connection to the panelboard grounding 
terminal as permitted in Section 384-20, Exception, so as 
to terminate within the same building or structure directly at 
an equipment grounding conductor terminal of the applicable 
derived system or service. 

FPN: Use of an isolated equipment grounding conductor 
does not relieve the requirement for grounding the raceway 
system and outlet box. 

250-148. Continuity and Attachment of Equipment 
Grounding Conductors to Boxes. Where more than one 
equipment grounding conductor enters a box, all such con- 
ductors shall be spliced or joined within the box or to the 
box with devices suitable for the use. Connections depending 
solely on solder shall not be used. Splices shall be made in 
accordance with Section 110- 14(b) except that insulation 
shall not be required. The arrangement of grounding connec- 
tions shall be such that the disconnection or the removal of 
a receptacle, fixture, or other device fed from the box will 
not interfere with or interrupt the grounding continuity. 

Exception: The equipment grounding conductor permitted 
in Section 250-146(d) shall not be required to be connected 
to the other equipment grounding conductors or to the box. 

(a) Metal Boxes. A connection shall be made between the 
one or more equipment grounding conductors and a metal 
box by means of a grounding screw that shall be used for 
no other purpose or a listed grounding device. 

(b) Nonmetallic Boxes. One or more equipment grounding 
conductors brought into a nonmetallic outlet box shall be 
arranged so that a connection can be made to any fitting or 
device in that box requiring grounding. 

H. Direct-Current Systems 

250-160. General. Direct-current systems shall comply 
with Part H and other sections of Article 250 not specifically 
intended for ac systems. 



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NATIONAL ELECTRICAL CODE 



ARTICLE 250 — GROUNDING 



70-101 



250-162. Direct-Current Circuits and Systems to Be 
Grounded. Direct-current circuits and systems shall be 
grounded as provided for in (a) and (b). 

(a) Two- Wire, Direct-Current Systems. A two-wire, dc 
system supplying premises wiring and operating at greater 
than 50 volts but not greater than 300 volts, shall be 
grounded. 

Exception No. 1: A system equipped with a ground detector 
and supplying only industrial equipment in limited areas 
shall not be required to be grounded. 

Exception No. 2: A rectifier-derived dc system supplied from 
an ac system complying with Section 250-20 shall not be 
required to be grounded. 

Exception No. 3: Direct-current fire alarm circuits having 
a maximum current of 0.030 amperes as specified in Article 
760, Part C, shall not be required to be grounded. 

(b) Three-Wire, Direct-Current Systems. The neutral 
conductor of all 3-wire, dc systems supplying premises wir- 
ing shall be grounded. 

250-164. Point of Connection for Direct-Current 
Systems. 

(a) Off-Premises Source. Direct-current systems to be 
grounded and supplied from an off-premises source shall 
have the grounding connection made at one or more supply 
stations. A grounding connection shall not be made at indi- 
vidual services or at any point on the premises wiring. 

(b) On-Premises Source. Where the dc system source is 
located on the premises, a grounding connection shall be 
made at one of the following: 

(1) The source 

(2) The first system disconnection means or overcurrent 
device 

(3) By other means that accomplish equivalent system pro- 
tection and that utilize equipment listed and identified 
for the use 

250-166. Size of Direct-Current Grounding Electrode 
Conductor. The size of the grounding electrode conductor 
for a dc system shall be as specified in (a) through (e). 

(a) Not Smaller than the Neutral Conductor. Where the 
dc system consists of a 3-wire balancer set or a balancer 
winding with overcurrent protection as provided in Section 
445-4(d), the grounding electrode conductor shall not be 
smaller than the neutral conductor, and not smaller than No. 
8 copper or No. 6 aluminum. 

(b) Not Smaller than the Largest Conductor. Where the 
dc system is other than as in (a), the grounding electrode 



conductor shall not be smaller than the largest conductor 
supplied by the system, and not smaller than No. 8 copper 
or No. 6 aluminum. 

(c) Connected to Made Electrodes. Where connected to 
made electrodes as in Section 250-52(c) or (d), that portion 
of the grounding electrode conductor that is the sole connec- 
tion to the grounding electrode shall not be required to be 
larger than No. 6 copper wire or No. 4 aluminum wire. 

(d) Connected to a Concrete-Encased Electrode. Where 
connected to a concrete-encased electrode as in Section 250- 
50(c), that portion of the grounding electrode conductor that 
is the sole connection to the grounding electrode shall not 
be required to be larger than No. 4 copper wire. 

(e) Connected to a Ground Ring. Where connected to a 
ground ring as in Section 250-50(d), that portion of the 
grounding electrode conductor that is the sole connection 
to the grounding electrode shall not be required to be larger 
than the conductor used for the ground ring. 

250-168. Direct-Current Bonding Jumper. For dc sys- 
tems, the size of the bonding jumper shall not be smaller 
than the system grounding conductor specified in Section 
250-166. 

250-169. Ungrounded Direct-Current Separately De- 
rived Systems. Except as otherwise permitted in Section 
250-34 for portable and vehicle mounted generators, an un- 
grounded dc separately derived system supplied from a 
stand-alone power source (such as an engine-generator set) 
shall have a grounding electrode conductor connected to an 
electrode that complies with Part C to provide for grounding 
of metal enclosures, raceways, cables, and exposed noncur- 
rent-carrying metal parts of equipment. The grounding elec- 
trode conductor connection shall be to the metal enclosure 
at any point on the separately derived system from the source 
to the first system disconnecting means or overcurrent de- 
vice, or it shall be made at the source of a separately derived 
system that has no disconnecting means or overcurrent de- 
vices. 

The size of the grounding electrode conductor shall be 
in accordance with Section 250-166. 

J. Instruments, Meters, and Relays 

250-170. Instrument Transformer Circuits. Secondary 
circuits of current and potential instrument transformers shall 
be grounded where the primary windings are connected to 
circuits of 300 volts or more to ground and, where on switch- 
boards, shall be grounded irrespective of voltage. 

Exception: Circuits where the primary windings are con- 
nected to circuits of less than 1000 volts with no live parts or 
wiring exposed or accessible to other than qualified persons. 



NATIONAL ELECTRICAL CODE 



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70-102 



ARTICLE 250 — GROUNDING 



250-172. Instrument Transformer Cases. Cases or frames 
of instrument transformers shall be grounded where accessi- 
ble to other than qualified persons. 

Exception: Cases or frames of current transformers, the 
primaries of which are not over 150 volts to ground and 
that are used exclusively to supply current to meters. 

250-174. Cases of Instruments, Meters, and Relays Op- 
erating at Less than 1000 Volts. Instruments, meters, and 
relays operating with windings or working parts at less than 
1000 volts shall be grounded as specified in (a), (b), or (c). 

(a) Not on Switchboards. Instruments, meters, and relays 
not located on switchboards, operating with windings or 
working parts at 300 volts or more to ground, and accessible 
to other than qualified persons, shall have the cases and 
other exposed metal parts grounded. 

(b) On Dead-Front Switchboards. Instruments, meters, 
and relays (whether operated from current and potential 
transformers or connected directly in the circuit) on switch- 
boards having no live parts on the front of the panels shall 
have the cases grounded. 

(c) On Live-Front Switchboards. Instruments, meters, 
and relays (whether operated from current and potential 
transformers or connected directly in the circuit) on switch- 
boards having exposed live parts on the front of panels shall 
not have their cases grounded. Mats of insulating rubber 
or other suitable floor insulation shall be provided for the 
operator where the voltage to ground exceeds 150. 

250-176. Cases of Instruments, Meters, and Relays — 
Operating Voltage 1 kV and Over. Where instruments, 
meters, and relays have current-carrying parts of 1 kV and 
over to ground, they shall be isolated by elevation or pro- 
tected by suitable barriers, grounded metal, or insulating 
covers or guards. Their cases shall not be grounded. 

Exception: Cases of electrostatic ground detectors where 
the internal ground segments of the instrument are connected 
to the instrument case and grounded and the ground detector 
is isolated by elevation. 

250-178. Instrument Grounding Conductor. The ground- 
ing conductor for secondary circuits of instrument transform- 
ers and for instrument cases shall not be smaller than No. 12 
copper or No. 10 aluminum. Cases of instrument transform- 
ers, instruments, meters, and relays that are mounted directly 
on grounded metal surfaces of enclosures or grounded metal 
switchboard panels shall be considered to be grounded, and 
no additional grounding conductor shall be required. 



K. Grounding of Systems and Circuits of 1 kV and Over 
(High Voltage) 

250-180. General. Where high-voltage systems are 
grounded, they shall comply with all applicable provisions of 
the preceding sections of this article and with the following 
sections, which supplement and modify the preceding sec- 
tions. 

250-182. Derived Neutral Systems. A system neutral de- 
rived from a grounding transformer shall be permitted to be 
used for grounding high-voltage systems. 

250-184. Solidly Grounded Neutral Systems. 

(a) Neutral Conductor. The minimum insulation level for 
neutral conductors of solidly grounded systems shall be 600 
volts. 

Exception No. 1: Bare copper conductors shall be permitted 
to be used for the neutral of service entrances and the neutral 
of direct-buried portions of feeders. 

Exception No. 2: Bare conductors shall be permitted for 
the neutral of overhead portions installed outdoors. 

FPN: See Section 225-4 for conductor covering where 
within 10 ft (3.05 m) of any building or other structure. 

(b) Multiple Grounding. The neutral of a solidly grounded 
neutral system shall be permitted to be grounded at more 
than one point for the following: 

(1) Services 

(2) Direct-buried portions of feeders employing a bare cop- 
per neutral 

(3) Overhead portion installed outdoors 

(c) Neutral Grounding Conductor. The neutral grounding 
conductor shall be permitted to be a bare conductor if isolated 
from phase conductors and protected from physical damage. 

250-186. Impedance Grounded Neutral Systems. Im- 
pedance grounded neutral systems shall comply with the 
provisions of (a) through (d). 

(a) Location. The grounding impedance shall be inserted 
in the grounding conductor between the grounding electrode 
of the supply system and the neutral point of the supply 
transformer or generator. 

(b) Identified and Insulated. Where the neutral conductor 
of an impedance grounded neutral system is used, it shall 
be identified, as well as fully insulated with the same insula- 
tion as the phase conductors. 

(c) System Neutral Connection. The system neutral shall 
not be connected to ground, except through the neutral 
grounding impedance. 



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ARTICLE 280 — SURGE ARRESTERS 



70-103 



(d) Equipment Grounding Conductors. Equipment 
grounding conductors shall be permitted to be bare and shall 
be connected to the ground bus and grounding electrode 
conductor at the service-entrance equipment or the 
disconnecting means for a separately derived system and 
extended to the system ground. 

250-188. Grounding of Systems Supplying Portable or 
Mobile Equipment. Systems supplying portable or mobile 
high-voltage equipment, other than substations installed on 
a temporary basis, shall comply with (a) through (f). 

(a) Portable or Mobile Equipment. Portable or mobile 
high-voltage equipment shall be supplied from a system 
having its neutral grounded through an impedance. Where 
a delta-connected high-voltage system is used to supply 
portable or mobile equipment, a system neutral shall be 
derived. 

(b) Exposed Noncurrent-Carrying Metal Parts. Ex- 
posed noncurrent-carrying metal parts of portable or mobile 
equipment shall be connected by an equipment grounding 
conductor to the point at which the system neutral impedance 
is grounded. 

(c) Ground-Fault Current. The voltage developed be- 
tween the portable or mobile equipment frame and ground 
by the flow of maximum ground-fault current shall not ex- 
ceed 100 volts. 

(d) Ground-Fault Detection and Relaying. Ground-fault 
detection and relaying shall be provided to automatically 
de-energize any high-voltage system component that has 
developed a ground fault. The continuity of the equipment 
grounding conductor shall be continuously monitored so as 
to de-energize automatically the high-voltage circuit to the 
portable or mobile equipment upon loss of continuity of the 
equipment grounding conductor. 

(e) Isolation. The grounding electrode to which the porta- 
ble or mobile equipment system neutral impedance is con- 
nected shall be isolated from and separated in the ground 
by at least 20 ft (6. 1 m) from any other system or equipment 
grounding electrode, and there shall be no direct connection 
between the grounding electrodes, such as buried pipe, fence, 
etc. 

(f) Trailing Cable and Couplers. High-voltage trailing 
cable and couplers for interconnection of portable or mobile 
equipment shall meet the requirements of Part C of Article 
400 for cables and Section 490-55 for couplers. 

250-190. Grounding of Equipment. All noncurrent-car- 
rying metal parts of fixed, portable, and mobile equipment 
and associated fences, housings, enclosures, and supporting 
structures shall be grounded. 



Exception: Where isolated from ground and located so as 
to prevent any person who can make contact with ground 
from contacting such metal parts when the equipment is 
energized. 

Grounding conductors not an integral part of a cable 
assembly shall not be smaller than No. 6 copper or No. 4 
aluminum. 

FPN: See Section 250-110, Exception No. 2 for pole- 
mounted distribution apparatus. 

Article 280 — Surge Arresters 

A. General 

280-1. Scope. This article covers general requirements, in- 
stallation requirements, and connection requirements for 
surge arresters installed on premises wiring systems. 

280-2. Definition. A surge arrester is a protective device 
for limiting surge voltages by discharging or bypassing surge 
current, and it also prevents continued flow of follow current 
while remaining capable of repeating these functions. 

280-3. Number Required. Where used at a point on a 
circuit, a surge arrester shall be connected to each un- 
grounded conductor. A single installation of such surge ar- 
resters shall be permitted to protect a number of 
interconnected circuits, provided that no circuit is exposed 
to surges while disconnected from the surge arresters. 

280-4. Surge Arrester Selection. 

(a) Circuits of Less than 1000 Volts. The rating of the 
surge arrester shall be equal to or greater than the maximum 
continuous phase-to-ground power frequency voltage avail- 
able at the point of application. 

Surge arresters installed on circuits of less than 1000 
volts shall be listed for the purpose. 

(b) Circuits of 1 kV and Over — Silicon Carbide Types. 

The rating of a silicon carbide-type surge arrester shall be 
not less than 125 percent of the maximum continuous phase- 
to-ground voltage available at the point of application. 

FPN No. 1: For further information on surge arresters, see 
Standard for Gapped Silicon-Carbide Surge Arresters for 
AC Power Circuits, ANSI/IEEE C62.l-l9S9„Guide for the 
Application of Gapped Silicon-Carbide Surge Arresters for 
Alternating-Current Systems, ANSI/IEEE C62.2-1987; 
Standard for Metal-Oxide Surge Arresters for Alternating- 
Current Power Circuits, ANSI/IEEE C62.1 1-1993; and 
Guide for the Application of Metal-Oxide Surge Arresters 
for Alternating-Current Systems, ANSI/IEEE C62.22-1991. 

FPN No. 2: The selection of a properly rated metal oxide 
arrester is based on considerations of maximum continuous 
operating voltage and the magnitude and duration of over- 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-104 



ARTICLE 280 — SURGE ARRESTERS 



voltages at the arrester location as affected by phase-to- 
ground faults, system grounding techniques, switching 
surges, and other causes. See the manufacturer's application 
rules for selection of the specific arrester to be used at a 
particular location. 



B. Installation 

280-11. Location. Surge arresters shall be permitted to be 
located indoors or outdoors. Surge arresters shall be made 
inaccessible to unqualified persons, unless listed for installa- 
tion in accessible locations. 

280-12. Routing of Surge Arrester Connections. The 

conductor used to connect the surge arrester to line or bus 
and to ground shall not be any longer than necessary and 
shall avoid unnecessary bends. 



C. Connecting Surge Arresters 

280-21. Installed at Services of Less than 1000 Volts. 

Line and ground connecting conductors shall not be smaller 
than No. 14 copper or No. 12 aluminum. The arrester ground- 
ing conductor shall be connected to one of the following: 

(1) Grounded service conductor 

(2) Grounding electrode conductor 

(3) Grounding electrode for the service 

(4) Equipment grounding terminal in the service equipment 

280-22. Installed on the Load Side Services of Less than 
1000 Volts. Line and ground connecting conductors shall 
not be smaller than No. 14 copper or No. 12 aluminum. A 
surge arrester shall be permitted to be connected between 
any two conductors — ungrounded conductor(s), grounded 
conductor, grounding conductor. The grounded conductor 
and the grounding conductor shall be interconnected only 
by the normal operation of the surge arrester during a surge. 

280-23. Circuits of 1 kV and Over — Surge-Arrester 
Conductors. The conductor between the surge arrester and 
the line and the surge arrester and the grounding connection 
shall not be smaller than No. 6 copper or aluminum. 

280-24. Circuits of 1 kV and Over — Interconnec- 
tions. The grounding conductor of a surge arrester pro- 
tecting a transformer that supplies a secondary distribution 
system shall be interconnected as specified in (a), (b), or (c). 



(a) Metallic Interconnections. A metallic interconnection 
shall be made to the secondary grounded circuit conductor 
or the secondary circuit grounding conductor provided that, 
in addition to the direct grounding connection at the surge 
arrester, the following occurs. 

(1) The grounded conductor of the secondary has else- 
where a grounding connection to a continuous metal under- 
ground water piping system. However, in urban water-pipe 
areas where there are at least four water-pipe connections 
on the neutral and not fewer than four such connections in 
each mile of neutral, the metallic interconnection shall be 
permitted to be made to the secondary neutral with omission 
of the direct grounding connection at the surge arrester. 

(2) The grounded conductor of the secondary system is 
a part of a multiground neutral system of which the primary 
neutral has at least four ground connections in each mile of 
line in addition to a ground at each service. 

(b) Through Spark Gap or Device. Where the surge ar- 
rester grounding conductor is not connected as in (a) or 
where the secondary is not grounded as in (a) but is otherwise 
grounded as in Sections 250-50 and 250-52, an inter- 
connection shall be made through a spark gap or listed device 
as follows. 

(1) For ungrounded or unigrounded primary systems, the 
spark gap or listed device shall have a 60-Hz breakdown 
voltage of at least twice the primary circuit voltage but not 
necessarily more than 10 kV, and there shall be at least one 
other ground on the grounded conductor of the secondary 
that is not less than 20 ft (6.1 m) distant from the surge 
arrester grounding electrode. 

(2) For multigrounded neutral primary systems, the spark 
gap or listed device shall have a 60-Hz breakdown of not 
more than 3 kV, and there shall be at least one other ground 
on the grounded conductor of the secondary that is not less 
than 20 ft (6. 1 m) distant from the surge arrester grounding 
electrode. 

(c) By Special Permission. An interconnection of the surge 
arrester ground and the secondary neutral, other than as 
provided in (a) or (b), shall be permitted to be made only 
by special permission. 

280-25. Grounding. Except as indicated in this article, 
surge arrester grounding connections shall be made as spec- 
ified in Article 250. Grounding conductors shall not be run 
in metal enclosures unless bonded to both ends of such 
enclosure. 



1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 300 — WIRING METHODS 



70-105 



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CHAPTER 3 
Wiring Methods and Materials 

Article 300 — Wiring Methods 

A. General Requirements 
300-1. Scope. 

(a) All Wiring Installations. This article covers wiring 
methods for all wiring installations unless modified by other 
articles. 

(b) Integral Parts of Equipment. The provisions of this 
article are not intended to apply to the conductors that form 
an integral part of equipment, such as motors, controllers, 
motor control centers, or factory assembled control equip- 
ment or listed utilization equipment. 

300-2. Limitations. 

(a) Voltage. Wiring methods specified in Chapter 3 shall 
be used for voltages 600 volts, nominal, or less where not 
specifically limited in some section of Chapter 3. They shall 
be permitted for voltages over 600 volts, nominal, where 
specifically permitted elsewhere in this Code. 

(b) Temperature. Temperature limitation of conductors 
shall be in accordance with Section 310-10. 

300-3. Conductors. 

(a) Single Conductors. Single conductors specified in 
Table 310-13 shall only be installed where part of a recog- 
nized wiring method of Chapter 3. 

(b) Conductors of the Same Circuit. All conductors of 
the same circuit and, where used, the grounded conductor 
and all equipment grounding conductors shall be contained 
within the same raceway, auxiliary gutter, cable tray, trench, 
cable, or cord, unless otherwise permitted in accordance 
with (1) through (4). 

(1) Paralleled Installations. Conductors shall be per- 
mitted to be run in parallel in accordance with the provisions 
of Section 3 10-4. The requirement to run all circuit conduc- 
tors within the same raceway, auxiliary gutter, cable tray, 
trench, cable, or cord shall apply separately to each portion 
of the paralleled installation, and the equipment grounding 
conductors shall comply with the provisions of Section 250- 
122. Parallel runs in cable tray shall comply with the provi- 
sions of Section 318-8(d). 

Exception: Conductors installed in nonmetallic raceways 
run underground shall be permitted to be arranged as iso- 
lated phase installations. The raceways shall be installed in 



close proximity and the conductors shall comply with the 
provisions of Section 300-20(b). 

(2) Grounding Conductors. Equipment grounding con- 
ductors shall be permitted to be installed outside a raceway 
or cable assembly where in accordance with the provisions 
of Section 250- 130(c) for certain existing 'installations, or 
in accordance with Section 250- 134(b), Exception No. 2, 
for dc circuits. Equipment bonding conductors shall be per- 
mitted to be installed on the outside of raceways in accor- 
dance with Section 250- 102(e). 

(3) Nonferrous Wiring Methods. Conductors in wiring 
methods with a nonmetallic or other nonmagnetic sheath 
shall, where run in different raceways, auxiliary gutters, 
cable trays, trenches, cables, or cords, comply with the pro- 
visions of Section 300-20(b). Conductors in single-conduc- 
tor Type MI cable with a nonmagnetic sheath shall comply 
with the provisions of Section 330-16. 

(4) Enclosures. Where an auxiliary gutter runs between 
a column-width panelboard and a pull box, and the pull 
box includes neutral terminations, the neutral conductors of 
circuits supplied from the panelboard shall be permitted to 
originate in the pull box. 

(c) Conductors of Different Systems. 

(1) 600 Volts, Nominal, or Less. Conductors of circuits 
rated 600 volts, nominal, or less, ac circuits, and dc circuits 
shall be permitted to occupy the same equipment wiring 
enclosure, cable, or raceway. All conductors shall have an 
insulation rating equal to at least the maximum circuit volt- 
age applied to any conductor within the enclosure, cable, or 
raceway. 

Exception: For solar photovoltaic systems in accordance 
with Section 690 -4(b). 

FPN: See Section 725-54(a)(l) for Class 2 and Class 3 
circuit conductors. 

(2) Over 600 Volts, Nominal. Conductors of circuits 
rated over 600 volts, nominal, shall not occupy the same 
equipment wiring enclosure, cable, or raceway with conduc- 
tors of circuits rated 600 volts, nominal, or less unless other- 
wise permitted in (a) through (e). 

(a) Secondary wiring to electric-discharge lamps of 1000 
volts or less, if insulated for the secondary voltage involved, 
shall be permitted to occupy the same fixture, sign, or outline 
lighting enclosure as the branch-circuit conductors. 

(b) Primary leads of electric-discharge lamp ballasts, 
insulated for the primary voltage of the ballast, where con- 
tained within the individual wiring enclosure, shall be per- 
mitted to occupy the same fixture, sign, or outline lighting 
enclosure as the branch-circuit conductors. 



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70-106 



ARTICLE 300 — WIRING METHODS 



(c) Excitation, control, relay, and ammeter conductors 
used in connection with any individual motor or starter shall 
be permitted to occupy the same enclosure as the motor- 
circuit conductors. 

(d) In motors, switchgear and control assemblies, and 
similar equipment, conductors of different voltage ratings 
shall be permitted. 

(e) In manholes, if the conductors of each system are 
permanently and effectively separated from the conductors 
of the other systems and securely fastened to racks, insula- 
tors, or other approved supports, conductors of different 
voltage ratings shall be permitted. 

Conductors having nonshielded insulation and operating 
at different voltage levels shall not occupy the same enclo- 
sure, cable, or raceway. 

300-4. Protection Against Physical Damage. Where sub- 
ject to physical damage, conductors shall be adequately pro- 
tected. 

(a) Cables and Raceways Through Wood Members. 

(1) Bored Holes. In both exposed and concealed loca- 
tions, where a cable or raceway-type wiring method is in- 
stalled through bored holes in joists, rafters, or wood 
members, holes shall be bored so that the edge of the hole 
is not less than V-A in. (31.8 mm) from the nearest edge of 
the wood member. Where this distance cannot be maintained, 
the cable or raceway shall be protected from penetration by 
screws or nails by a steel plate or bushing, at least J /i6 in. 
(1.59 mm) thick, and of appropriate length and width in- 
stalled to cover the area of the wiring. 

Exception: Steel plates shall not be required to protect rigid 
metal conduit, intermediate metal conduit, rigid nonmetallic 
conduit, or electrical metallic tubing. 

(2) Notches in Wood. Where there is no objection be- 
cause of weakening the building structure, in both exposed 
and concealed locations, cables or raceways shall be permit- 
ted to be laid in notches in wood studs, joists, rafters, or 
other wood members where the cable or raceway at those 
points is protected against nails or screws by a steel plate 
at least !/i6 in. (1.59 mm) thick installed before the building 
finish is applied. 

Exception: Steel plates shall not be required to protect rigid 
metal conduit, intermediate metal conduit, rigid nonmetallic 
conduit, or electrical metallic tubing. 

(b) Nonmetallic-Sheathed Cables and Electrical Non- 
metallic Tubing Through Metal Framing Members. 

(1) Nonmetallic-Sheathed Cable. In both exposed and 
concealed locations where nonmetallic-sheathed cables pass 
through either factory or field punched, cut, or drilled slots 
or holes in metal members, the cable shall be protected by 



bushings or grommets covering all metal edges and securely 
fastened in the opening prior to installation of the cable. 

(2) Nonmetallic-Sheathed Cable and Electrical Non- 
metallic Tubing. Where nails or screws are likely to pene- 
trate nonmetallic-sheathed cable or electrical nonmetallic 
tubing, a steel sleeve, steel plate, or steel clip not less than 
Vi6 in. (1.59 mm) in thickness shall be used to protect the 
cable or tubing. 

(c) Cables Through Spaces Behind Panels Designed to 
Allow Access. Cables or raceway-type wiring methods, in- 
stalled behind panels designed to allow access, shall be 
supported according to their applicable articles. 

(d) Cables and Raceways Parallel to Framing Members. 

In both exposed and concealed locations, where a cable- or 
raceway-type wiring method is installed parallel to framing 
members, such as joists, rafters, or studs, the cable or race- 
way shall be installed and supported so that the nearest 
outside surface of the cable or raceway is not less than 1 l A in. 
(31.8 mm) from the nearest edge of the framing member 
where nails or screws are likely to penetrate. Where this 
distance cannot be maintained, the cable or raceway shall 
be protected from penetration by nails or screws by a steel 
plate, sleeve, or equivalent at least '/i6 in. (1.59 mm) thick. 

Exception No. 1: Steel plates, sleeves, or the equivalent 
shall not be required to protect rigid metal conduit, interme- 
diate metal conduit, rigid nonmetallic conduit, or electrical 
metallic tubing. 

Exception No. 2: For concealed work in finished buildings, 
or finished panels for prefabricated buildings where such 
supporting is impracticable, it shall be permissible to fish 
the cables between access points. 

Exception No. 3: Steel plates, sleeves, or the equivalent 
shall not be required to protect cables or raceways in mobile 
homes and recreational vehicles. 

(e) Cables and Raceways Installed in Shallow Grooves. 

Cable- or raceway-type wiring methods installed in a groove, 
to be covered by wallboard, siding, paneling, carpeting, or 
similar finish, shall be protected by Vis in. (1.59 mm) thick 
steel plate, sleeve, or equivalent or by not less than 1 l A in. 
(31.8 mm) free space for the full length of the groove in 
which the cable or raceway is installed. 

Exception: Steel plates, sleeves, or the equivalent shall not 
be required to protect rigid metal conduit, intermediate metal 
conduit, rigid nonmetallic conduit, or electrical metallic 
tubing. 

(f) Insulated Fittings. Where raceways containing un- 
grounded conductors No. 4 or larger enter a cabinet, box 
enclosure, or raceway, the conductors shall be protected by 
a substantial fitting providing a smoothly rounded insulating 



• 



• 



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1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 300 — WIRING METHODS 



70-107 



surface, unless the conductors are separated from the fitting 
or raceway by substantial insulating material that is securely 
fastened in place. 

Exception: Where threaded hubs or bosses that are an inte- 
gral part of a cabinet, box enclosure, or raceway provide 
a smoothly rounded or flared entry for conductors. 

Conduit bushings constructed wholly of insulating mate- 
rial shall not be used to secure a fitting or raceway. The 
insulating fitting or insulating material shall have a tempera- 
ture rating not less than the insulation temperature rating of 
the installed conductors. 

300-5. Underground Installations. 

(a) Minimum Cover Requirements. Direct-buried cable 
or conduit or other raceways shall be installed to meet the 
minimum cover requirements of Table 300-5. 

(b) Grounding. All underground installations shall be 
grounded and bonded in accordance with Article 250. 

(c) Underground Cables Under Buildings. Underground 
cable installed under a building shall be in a raceway that 
is extended beyond the outside walls of the building. 

(d) Protection from Damage. Direct-buried conductors 
and cables emerging from the ground shall be protected by 
enclosures or raceways extending from the minimum cover 
distance required by Section 300-5(a) below grade to a point 
at least 8 ft (2.44 m) above finished grade. In no case shall 
the protection be required to exceed 18 in. (457 mm) below 
finished grade. 

Service laterals that are not encased in concrete and that 
are buried 18 in. (457 mm) or more below grade shall have 
their location identified by a warning ribbon that is placed 
in the trench at least 12 in. (305 mm) above the underground 
installation. 

Conductors entering a building shall be protected to the 
point of entrance. 

Where the enclosure or raceway is subject to physical 
damage, the conductors shall be installed in rigid metal 
conduit, intermediate metal conduit, Schedule 80 rigid 
nonmetallic conduit, or equivalent. 

(e) Splices and Taps. Direct-buried conductors or cables 
shall be permitted to be spliced or tapped without the use 
of splice boxes. The splices or taps shall be made in accor- 
dance with Section 110-14(b). 

(f) Backfill. Backfill that contains large rocks, paving ma- 
terials, cinders, large or sharply angular substances, or corro- 
sive material shall not be placed in an excavation where 
materials may damage raceways, cables, or other substruc- 
tures or prevent adequate compaction of fill or contribute 
to corrosion of raceways, cables, or other substructures. 



Where necessary to prevent physical damage to the race- 
way or cable, protection shall be provided in the form of 
granular or selected material, suitable running boards, suit- 
able sleeves, or other approved means. 

(g) Raceway Seals. Conduits or raceways through which 
moisture may contact energized live parts shall be sealed or 
plugged at either or both ends. 

FPN: Presence of hazardous gases or vapors may also neces- 
sitate sealing of underground conduits or raceways entering 
buildings. 

(h) Bushing. A bushing, or terminal fitting, with an integral 
bushed opening shall be used at the end of a conduit or 
other raceway that terminates underground where the con- 
ductors or cables emerge as a direct burial wiring method. 
A seal incorporating the physical protection characteristics 
of a bushing shall be permitted to be used in lieu of a 
bushing. 

(i) Conductors of the Same Circuit. All conductors of the 
same circuit and, where used, the grounded conductor and 
all equipment grounding conductors shall be installed in the 
same raceway or shall be installed in close proximity in the 
same trench. 

Exception No. 1: Conductors in parallel in raceways shall 
be permitted, but each raceway shall contain all conductors 
of the same circuit including grounding conductors. 

Exception No. 2: Isolated phase installations shall be per- 
mitted in nonmetallic raceways in close proximity where 
conductors are paralleled as permitted in Section 310-4, 
and where the conditions of Section 300-20 are met. 

(j) Ground Movement. Where direct-buried conductors, 
raceways, or cables are subject to movement by settlement 
or frost, direct-buried conductors, raceways, or cables shall 
be arranged to prevent damage to the enclosed conductors 
or to equipment connected to the raceways. 

FPN: This section recognizes "S" loops in underground di- 
rect burial to raceway transitions, expansion joints in race- 
way risers to fixed equipment, and, generally, the provision 
of flexible connections to equipment subject to settlement 
or frost heaves. 

300-6. Protection Against Corrosion. Metal raceways, 
cable trays, cablebus, auxiliary gutters, cable armor, boxes, 
cable sheathing, cabinets, elbows, couplings, fittings, sup- 
ports, and support hardware shall be of materials suitable 
for the environment in which they are to be installed. 

(a) General. Ferrous raceways, cable trays, cablebus, aux- 
iliary gutters, cable armor, boxes, cable sheathing, cabinets, 
metal elbows, couplings, fittings, supports, and support hard- 
ware shall be suitably protected against corrosion inside and 



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1999 Edition 



70-108 



ARTICLE 300 — WIRING METHODS 



Table 300-5. Minimum Cover Requirements, to 600 Volts, Nominal, Burial in Inches (Cover 
is defined as the shortest distance in inches measured between a point on the top surface of any 
direct-buried conductor, cable, conduit, or other raceway and the top surface of finished grade, 
concrete, or similar cover.) 



• 



Type of Wiring Method or Circuit 



Location of Wiring 
Method or Circuit 



Column 1 

Direct Burial Cables 

or Conductors 



Column 2 

Rigid Metal Conduit 

or Intermediate Metal 

Conduit 



Column 3 

Nonmetallic Raceways 

Listed for Direct 

Burial Without 

Concrete Encasement 

or Other Approved 

Raceways 



Column 4 

Residential Branch 

Circuits Rated 120 

Volts or Less with 

GFCI Protection and 

Maximum 

Overcurrent 

Protection of 20 

Amperes 



Column 5 

Circuits for Control of 

Irrigation and 

Landscape Lighting 

Limited to Not More 

than 30 Volts and 

Installed with Type UF 

or in Other Identified 

Cable or Raceway 



All locations not speci- 
fied below 




24 


6 


18 


12 




6 


In trench below 2-in. 
thick concrete or 
equivalent 




18 


6 


12 


6 




6 


Under a building 


(in 


.0. 
raceway only) 









(in raceway only) 


(in 


. 
raceway only) 



• 



Under minimum of 4- 
in. thick concrete ex- 
terior slab with no 
vehicular traffic and 
the slab extending 
not less than 6 in. be- 
yond the under- 
ground installation 



18 



6 (direct burial) 
4 (in raceway) 



6 (direct burial) 
4 (in raceway) 



• 



Under streets, high- 
ways, roads, alleys, 
driveways, and park- 
ing lots 



24 



24 



24 



24 



24 



One- and two-family 
dwelling driveways 
and outdoor parking 
areas, and used only 
for dwelling-related 
purposes 



18 



12 



18 



In or under airport run- 
ways, including ad- 
jacent areas where 
trespassing 
prohibited 



18 



18 



18 



18 



Notes: 

1. For SI units, 1 in. = 25.4 mm. 

2. Raceways approved for burial only where concrete encased shall require concrete envelope not less 
than 2 in. thick. 

3. Lesser depths shall be permitted where cables and conductors rise for terminations or splices or where 
access is otherwise required. 

4. Where one of the wiring method types listed in Columns 1-3 is used for one of the circuit types in 
Columns 4 and 5, the shallower depth of burial shall be permitted. 

5. Where solid rock prevents compliance with the cover depths specified in this table, the wiring shall be 
installed in metal or nonmetallic raceway permitted for direct burial. The raceways shall be covered by 

a minimum of 2 in. of concrete extending down to rock. 



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ARTICLE 300 — WIRING METHODS 



70-109 



outside (except threads at joints) by a coating of approved 
corrosion-resistant material such as zinc, cadmium, or 
enamel. Where protected from corrosion solely by enamel, 
they shall not be used outdoors or in wet locations as de- 
scribed in (c). Where boxes or cabinets have an approved 
system of organic coatings and are marked "Raintight," 
"Rainproof," or "Outdoor Type," they shall be permitted 
outdoors. 

Exception: Threads at joints shall be permitted to be coated 
with an identified electrically conductive compound. 

(b) In Concrete or in Direct Contact with the Earth. Fer- 
rous or nonferrous metal raceways, cable armor, boxes, cable 
sheathing, cabinets, elbows, couplings, fittings, supports, 
and support hardware shall be permitted to be installed in 
concrete or in direct contact with the earth, or in areas subject 
to severe corrosive influences where made of material judged 
suitable for the condition, or where provided with corrosion 
protection approved for the condition. 

(c) Indoor Wet Locations. In portions of dairies, laundries, 
canneries, and other indoor wet locations, and in locations 
where walls are frequently washed or where there are sur- 
faces of absorbent materials, such as damp paper or wood, 
the entire wiring system, where installed exposed, including 
all boxes, fittings, conduits, and cable used therewith, shall 
be mounted so that there is at least a l /4-in. (6.35-mm) air- 
space between it and the wall or supporting surface. 

Exception: Nonmetallic raceways, boxes, and fittings shall 
be permitted to be installed without the airspace on a con- 
crete, masonry, tile, or similar surface. 

FPN: In general, areas where acids and alkali chemicals are 
handled and stored may present such corrosive conditions, 
particularly when wet or damp. Severe corrosive conditions 
may also be present in portions of meatpacking plants, tan- 
neries, glue houses, and some stables; installations immedi- 
ately adjacent to a seashore and swimming pool areas; areas 
where chemical deicers are used; and storage cellars or rooms 
for hides, casings, fertilizer, salt, and bulk chemicals. 

300-7. Raceways Exposed to Different Temperatures. 

(a) Sealing. Where portions of an interior raceway system 
are exposed to widely different temperatures, as in refriger- 
ating or cold-storage plants, circulation of air from a warmer 
to a colder section through the raceway shall be prevented. 

(b) Expansion Joints. Raceways shall be provided with 
expansion joints where necessary to compensate for thermal 
expansion and contraction. 

FPN: Table 347-9 provides the expansion information for 
polyvinyl chloride (PVC). A nominal number for steel con- 
duit can be determined by multiplying the expansion length 
in this table by 0.20. The coefficient of expansion for steel 
electrical metallic tubing, intermediate metal conduit, and 



rigid conduit is 6.50 X 10 -6 (0.0000065 in. per inch of 
conduit for each °F in temperature change). 



300-8. Installation of Conductors with Other Sys- 
tems. Raceways or cable trays containing electric conduc- 
tors shall not contain any pipe, tube, or equal for steam, 
water, air, gas, drainage, or any service other than electrical. 

300-10. Electrical Continuity of Metal Raceways and 
Enclosures. Metal raceways, cable armor, and other metal 
enclosures for conductors shall be metallically joined to- 
gether into a continuous electric conductor and shall be 
connected to all boxes, fittings, and cabinets so as to provide 
effective electrical continuity. Unless specifically permitted 
elsewhere in this Code, raceways and cable assemblies shall 
be mechanically secured to boxes, fittings, cabinets, and 
other enclosures. 

Exception: Short sections of raceways used to provide sup- 
port or protection of cable assemblies from physical damage 
shall not be required to be made electrically continuous. 

300-11. Securing and Supporting. 

(a) Secured in Place. Raceways, cable assemblies, boxes, 
cabinets, and fittings shall be securely fastened in place. 
Support wires that do not provide secure support shall not be 
permitted as the sole support. Support wires and associated 
fittings that provide secure support and that are installed in 
addition to the ceiling grid support wires, shall be permitted 
as the sole support. Where independent support wires are 
used, they shall be secured at both ends. Cables and raceways 
shall not be supported by ceiling grids. 

(1) Wiring located within the cavity of a fire-rated floor- 
ceiling or roof-ceiling assembly shall not be secured to, or 
supported by, the ceiling assembly, including the ceiling 
support wires. An independent means of secure support shall 
be provided. Where independent support wires are used, 
they shall be distinguishable by color, tagging, or other effec- 
tive means from those that are part of the fire-rated design. 

Exception: The ceiling support system shall be permitted 
to support wiring and equipment that have been tested as 
part of the fire-rated assembly. 

FPN: One method of determining fire rating is testing in 
accordance with Standard Methods of Tests of Fire Endur- 
ance of Building Construction and Materials, NFPA 251- 
1995. 



(2) Wiring located within the cavity of a nonfire-rated 
floor-ceiling or roof-ceiling assembly shall not be secured 
to, or supported by, the ceiling assembly, including the 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-110 



ARTICLE 300 — WIRING METHODS 



ceiling support wires. An independent means of secure sup- 
port shall be provided. 

Exception: The ceiling support system shall be permitted 
to support branch- circuit wiring and associated equipment 
where installed in accordance with the ceiling system man- 
ufacturer's instructions. 

(b) Raceways Used as Means of Support. Raceways shall 
only be used as a means of support for other raceways, 
cables, or nonelectric equipment under the following condi- 
tions: 

(1) Where the raceway or means of support is identified for 
the purpose; or 

(2) Where the raceway contains power supply conductors 
for electrically controlled equipment and is used to sup- 
port Class 2 circuit conductors or cables that are solely 
for the purpose of connection to the equipment control 
circuits; or 

(3) Where the raceway is used to support boxes or conduit- 
bodies in accordance with Section 370-23 or to support 
fixtures in accordance with Section 4 10- 16(f) 

300-12. Mechanical Continuity — Raceways and Cables. 

Metal or nonmetallic raceways, cable armors, and cable 
sheaths shall be continuous between cabinets, boxes, fittings, 
or other enclosures or outlets. 

Exception: Short sections of raceways used to provide sup- 
port or protection of cable assemblies from physical damage 
shall not be required to be mechanically continuous. 

300-13. Mechanical and Electrical Continuity — Con- 
ductors. 

(a) General. Conductors in raceways shall be continuous 
between outlets, boxes, devices, etc. There shall be no splice 
or tap within a raceway unless permitted by Sections 300- 
15; 352-7; 352-29; 354-6, Exception; 362-7; 362-21; or 364- 
8(a). 

(b) Device Removal. In multiwire branch circuits, the con- 
tinuity of a grounded conductor shall not depend on device 
connections such as lampholders, receptacles, etc., where 
the removal of such devices would interrupt the continuity. 

300-14. Length of Free Conductors at Outlets, Junctions, 
and Switch Points. At least 6 in. (152 mm) of free conduc- 
tor, measured from the point in the box where it emerges 
from its raceway or cable sheath, shall be left at each outlet, 
junction, and switch point for splices or the connection of 
fixtures or devices. Where the opening to an outlet, junction, 
or switch point is less than 8 in. (203 mm) in any dimension, 
each conductor shall be long enough to extend at least 3 in. 
(76.2 mm) outside the opening. 



Exception: Conductors that are not spliced or terminated 
at the outlet, junction, or switch point. 

300-15. Boxes, Conduit Bodies, or Fittings — Where 
Required. 

(a) Box or Conduit Body. Where the wiring method is 
conduit, electrical metallic tubing, Type AC cable, Type MC 
cable, Type MI cable, nonmetallic-sheathed cable, or other 
cables, a box or conduit body complying with Article 370 
shall be installed at each conductor splice point, outlet, 
switch point, junction point, or pull point, unless otherwise 
permitted in (b) through (n). A box shall be installed at each 
outlet and switch point for concealed knob-and-tube wiring. 

Fittings and connectors shall be used only with the spe- 
cific wiring methods for which they are designed and listed. 

(b) Equipment. An integral junction box or wiring com- 
partment as part of approved equipment shall be permitted. 

(c) Protection. Where cables enter or exit from conduit or 
tubing that is used to provide cable support or protection 
against physical damage. A fitting shall be provided on the 
end(s) of the conduit or tubing to protect the cable from 
abrasion. 

(d) Type MI Cable. Where accessible fittings are used for 
straight-through splices in mineral-insulated metal-sheathed 
cable. 

(e) Integral Enclosure. A wiring device with integral en- 
closure identified for the use, having brackets that securely 
fasten the device to walls or ceilings of conventional on- 
site frame construction, for use with nonmetallic-sheathed 
cable, shall be permitted in lieu of a box or conduit body. 

FPN: See Sections 336-18, Exception No. 2; 545-10; 550- 
10(i); and 551-47(e), Exception No. 1. 

(f) Fitting. A fitting identified for the use shall be permitted 
in lieu of a box or conduit body where accessible after 
installation and not containing spliced or terminated conduc- 
tors. 

(g) Buried Conductors. As permitted in Section 300-5(e) 
for splices and taps in buried conductors and cables. 

(h) Insulated Devices. As permitted in Section 336-21 for 
insulated devices supplied by nonmetallic-sheathed cable. 

(i) Enclosures. As permitted in Section 373-8 for switches 
and overcurrent devices, and Section 430- 10(a) for motor 
controllers. 

(j) Fixtures. As permitted in Section 410-31 where a fix- 
ture is used as a raceway. 



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ARTICLE 300 — WIRING METHODS 



70-111 



(k) Embedded. Where conductors are embedded as cov- 
ered in Sections 424-40, 424-4 1(d), 426-22(b), 426-24(a), 
and 427-19(a). 

(1) Manufactured Wiring System. Where manufactured 
wiring systems in accordance with Article 604 are used. 

(m) Closed Loop. Where a device identified and listed as 
suitable for installation without a box is used with a closed- 
loop power distribution system. 

(n) Manholes. A box or conduit body shall not be required 
for conductors in manholes where accessible only to quali- 
fied persons. 

300-16. Raceway or Cable to Open or Concealed 
Wiring. 

(a) Box or Fitting. A box or terminal fitting having a sep- 
arately bushed hole for each conductor shall be used wher- 
ever a change is made from conduit, electrical metallic 
tubing, electrical nonmetallic tubing, nonmetallic-sheathed 
cable, Type AC cable, Type MC cable, or mineral-insulated, 
metal-sheathed cable and surface raceway wiring to open 
wiring or to concealed knob-and-tube wiring. A fitting used 
for this purpose shall contain no taps or splices and shall 
not be used at fixture outlets. 

(b) Bushing. A bushing shall be permitted in lieu of a 
box or terminal fitting where the conductors emerge from 
a raceway or conduit and enter or terminate at equipment, 
such as open switchboards, unenclosed control equipment, 
or similar equipment. The bushing shall be of the insulating 
type for other than lead-sheathed conductors. 

300-17. Number and Size of Conductors in Race- 
way. The number and size of conductors in any raceway 
shall not be more than will permit dissipation of the heat and 
ready installation or withdrawal of the conductors without 
damage to the conductors or to their insulation. 

FPN: See the following sections of this Code: electrical 
nonmetallic tubing, Section 331-6; intermediate metal con- 
duit, Section 345-7; rigid metal conduit, Section 346-7; rigid 
nonmetallic conduit, Section 347-11; electrical metallic tub- 
ing, Section 348-8; flexible metallic tubing, Section 349-12; 
flexible metal conduit, Section 350-12; liquidtight flexible 
metal conduit, Section 351-6; liquidtight nonmetallic flexi- 
ble conduit, Section 351-25; surface raceways, Sections 352- 
4 and 352-25; underfloor raceways, Section 354-5; cellular 
metal floor raceways, Section 356-5; cellular concrete floor 
raceways, Section 358-11; wireways, Section 362-5; fixture 
wire, Section 402-7; theaters, Section 520-6; signs, Section 
600-3 1(c); elevators, Section 620-33; audio signal pro- 
cessing, amplification, and reproduction equipment, Sec- 
tions 640-23 (a) and 640-24; Class 1, Class 2, and Class 3 
circuits, Article 725; fire alarm circuits, Article 760, and 
optical fiber cables and raceways, Article 770. 



300-18. Raceway Installations. 

(a) Complete Runs. Raceways, other than busways or ex- 
posed raceways having hinged or removable covers, shall 
be installed complete between outlet, junction, or splicing 
points prior to the installation of conductors. Where required 
to facilitate the installation of utilization equipment, the 
raceway shall be permitted to be initially installed without 
a terminating connection at the equipment. Prewired raceway 
assemblies shall be permitted only where specifically per- 
mitted in this Code for the applicable wiring method. 



(b) Welding. Metal raceways shall not be supported, ter- 
minated, or connected by welding to the raceway unless 
specifically designed to be or otherwise specifically permit- 
ted to be in this Code. 

300-19. Supporting Conductors in Vertical Raceways. 

(a) Spacing Intervals — Maximum. Conductors in ver- 
tical raceways shall be supported if the vertical rise exceeds 
the values in Table 300- 19(a). One cable support shall be 
provided at the top of the vertical raceway or as close to 
the top as practical. Intermediate supports shall be provided 
as necessary to limit supported conductor lengths to not 
greater than those values specified in Table 300- 19(a). 

Exception: Steel wire armor cable shall be supported at the 
top of the riser with a cable support that clamps the steel 
wire armor. A safety device shall be permitted at the lower 
end of the riser to hold the cable in the event there is slippage 
of the cable in the wire-armored cable support. Additional 



Table 300-19(a). 


Spacings for Conductor Supports 






Support of 


Conductors 










Conductors 


Aluminum or 






in Vertical 


Copper-Clad 




Size of Wire 


Raceways 


Aluminum 


Copper 


18 AWG through 


Not greater than 


100 ft 


100 ft 


8 AWG 








6 AWG through 


Not greater than 


200 ft 


100 ft 


1/0 AWG 








2/0 AWG through 


Not greater than 


180 ft 


80 ft 


4/0 AWG 








Over 4/0 AWG 


Not greater than 


135 ft 


60 ft 


through 350 








kcmil 








Over 350 kcmil 


Not greater than 


120 ft 


50 ft 


through 500 








kcmil 








Over 500 kcmil 


Not greater than 


95 ft 


40 ft 


through 750 








kcmil 








Over 750 kcmil 


Not greater than 


85 ft 


35 ft 


Note: For SI units, 


1 ft = 0.3048 m. 







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70-112 



ARTICLE 300 — WIRING METHODS 



wedge-type supports shall be permitted to relieve the strain 
on the equipment terminals caused by expansion of the cable 
under load. 

(b) Support Methods. One of the following methods of 
support shall be used. 

(1) By clamping devices constructed of or employing 
insulating wedges inserted in the ends of the raceways. 
Where clamping of insulation does not adequately support 
the cable, the conductor also shall be clamped. 

(2) By inserting boxes at the required intervals in which 
insulating supports are installed and secured in a satisfactory 
manner to withstand the weight of the conductors attached 
thereto, the boxes being provided with covers. 

(3) In junction boxes, by deflecting the cables not less 
than 90 degrees and carrying them horizontally to a distance 
not less than twice the diameter of the cable, the cables being 
carried on two or more insulating supports and additionally 
secured thereto by tie wires if desired. Where this method 
is used, cables shall be supported at intervals not greater than 
20 percent of those mentioned in the preceding tabulation. 

(4) By a method of equal effectiveness. 

300-20. Induced Currents in Metal Enclosures or Metal 
Raceways. 

(a) Conductors Grouped Together. Where conductors 
carrying alternating current are installed in metal enclosures 
or metal raceways, they shall be arranged so as to avoid 
heating the surrounding metal by induction. To accomplish 
this, all phase conductors and, where used, the grounded 
conductor and all equipment grounding conductors shall be 
grouped together. 

Exception No. 1: Equipment grounding conductors for cer- 
tain existing installations shall be permitted to be installed 
separate from their associated circuit conductors where run 
in accordance with the provisions of Section 250-130(c). 

Exception No. 2: A single conductor shall be permitted to 
be installed in a ferromagnetic enclosure and used for skin- 
effect heating in accordance with the provisions of Sections 
426-42 and 427-47. 

(b) Individual Conductors. Where a single conductor car- 
rying alternating current passes through metal with magnetic 
properties, the inductive effect shall be minimized by (1) 
cutting slots in the metal between the individual holes 
through which the individual conductors pass, or (2) passing 
all the conductors in the circuit through an insulating wall 
sufficiently large for all of the conductors of the circuit. 

Exception: In the case of circuits supplying vacuum or elec- 
tric-discharge lighting systems or signs, or X-ray apparatus, 



the currents carried by the conductors are so small that the 
inductive heating effect can be ignored where these conduc- 
tors are placed in metal enclosures or pass through metal. 

FPN: Because aluminum is not a magnetic metal, there will 
be no heating due to hysteresis; however, induced currents 
will be present. They will not be of sufficient magnitude to 
require grouping of conductors or special treatment in pass- 
ing conductors through aluminum wall sections. 

300-21. Spread of Fire or Products of Combustion. Elec- 
trical installations in hollow spaces, vertical shafts, and ven- 
tilation or air-handling ducts shall be made so that the 
possible spread of fire or products of combustion will not 
be substantially increased. Openings around electrical 
penetrations through fire-resistant-rated walls, partitions, 
floors, or ceilings shall be firestopped using approved meth- 
ods to maintain the fire resistance rating. 

FPN: Directories of electrical construction materials pub- 
lished by qualified testing laboratories contain many listing 
installation restrictions necessary to maintain the fire- 
resistive rating of assemblies where penetrations or openings 
are made. An example is the 24-in. (610-mm) minimum 
horizontal separation that usually applies between boxes on 
opposite sides of the wall. Assistance in complying with 
Section 300-21 can be found in these directories and product 
listings. 

300-22. Wiring in Ducts, Plenums, and Other Air- 
Handling Spaces. The provisions of this section apply to 
the installation and uses of electric wiring and equipment 
in ducts, plenums, and other air-handling spaces. 

FPN: Article 424, Part F. 

(a) Ducts for Dust, Loose Stock, or Vapor Removal. No 

wiring systems of any type shall be installed in ducts used to 
transport dust, loose stock, or flammable vapors. No wiring 
system of any type shall be installed in any duct, or shaft 
containing only such ducts, used for vapor removal or for 
ventilation of commercial-type cooking equipment. 

(b) Ducts or Plenums Used for Environmental Air. Only 
wiring methods consisting of Type MI cable, Type MC cable 
employing a smooth or corrugated impervious metal sheath 
without an overall nonmetallic covering, electrical metallic 
tubing, flexible metallic tubing, intermediate metal conduit, 
or rigid metal conduit shall be installed in ducts or plenums 
specifically fabricated to transport environmental air. Flexi- 
ble metal conduit and liquidtight flexible metal conduit shall 
be permitted, in lengths not to exceed 4 ft (1.22 m), to 
connect physically adjustable equipment and devices permit- 
ted to be in these ducts and plenum chambers. The connectors 
used with flexible metal conduit shall effectively close any 
openings in the connection. Equipment and devices shall be 
permitted within such ducts or plenum chambers only if 
necessary for their direct action upon, or sensing of, the 



• 



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ARTICLE 300 — WIRING METHODS 



70-113 



contained air. Where equipment or devices are installed and 
illumination is necessary to facilitate maintenance and repair, 
enclosed gasketed-type fixtures shall be permitted. 

(c) Other Space Used for Environmental Air. This sec- 
tion applies to space used for environmental air-handling 
purposes other than ducts and plenums as specified in (a) 
and (b). It does not include habitable rooms or areas of 
buildings, the prime purpose of which is not air handling. 

FPN: The space over a hung ceiling used for environmental 
air-handling purposes is an example of the type of other 
space to which this section applies. 

Exception: This section shall not apply to the joist or stud 
spaces of dwelling units where the wiring passes through 
such spaces perpendicular to the long dimension of such 
spaces. 

(1) Wiring Methods. The wiring methods for such other 
space shall be limited to totally enclosed, nonventilated, 
insulated busway having no provisions for plug-in connec- 
tions, Type MI cable, Type MC cable without an overall 
nonmetallic covering, Type AC cable, or other factory-as- 
sembled multiconductor control or power cable that is 
specifically listed for the use, or listed prefabricated cable 
assemblies of metallic manufactured wiring systems without 
nonmetallic sheath. Other type cables and conductors shall 
be installed in electrical metallic tubing, flexible metallic 
tubing, intermediate metal conduit, rigid metal conduit, flex- 
ible metal conduit, or, where accessible, surface metal race- 
way or metal wireway with metal covers or solid bottom 
metal cable tray with solid metal covers. 

Exception: Liquidtight flexible metal conduit shall be per- 
mitted in single lengths not exceeding 6 ft (1.83 m). 

(2) Equipment. Electrical equipment with a metal en- 
closure, or with a nonmetallic enclosure listed for the use 
and having adequate fire-resistant and low-smoke-producing 
characteristics, and associated wiring material suitable for 
the ambient temperature shall be permitted to be installed 
in such other space unless prohibited elsewhere in this Code. 

Exception: Integral fan systems shall be permitted where 
specifically identified for such use. 

(d) Information Technology Equipment. Electric wiring 
in air-handling areas beneath raised floors for information 
technology equipment shall be permitted in accordance with 
Article 645. 

300-23. Panels Designed to Allow Access. Cables, race- 
ways, and equipment installed behind panels designed to 
allow access, including suspended ceiling panels, shall be 
arranged and secured so as to allow the removal of panels 
and access to the equipment. 



B. Requirements for Over 600 Volts, Nominal 

300-31. Covers Required. Suitable covers shall be in- 
stalled on all boxes, fittings, and similar enclosures to pre- 
vent accidental contact with energized parts or physical 
damage to parts or insulation. 

300-32. Conductors of Different Systems. See Section 
300-3(c)(2). 

300-34. Conductor Bending Radius. The conductor shall 
not be bent to a radius less than 8 times the overall diameter 
for nonshielded conductors or 12 times the diameter for 
shielded or lead-covered conductors during or after installa- 
tion. For multiconductor or multiplexed single conductor 
cables having individually shielded conductors, the mini- 
mum bending radius is 12 times the diameter of the individu- 
ally shielded conductors or 7 times the overall diameter, 
whichever is greater. 

300-35. Protection Against Induction Heating. Metallic 
raceways and associated conductors shall be arranged so as 
to avoid heating of the raceway in accordance with the 
applicable provisions of Section 300-20. 



300-37. Aboveground Wiring Methods. Aboveground 
conductors shall be installed in rigid metal conduit, in inter- 
mediate metal conduit, in electrical metallic tubing, in rigid 
nonmetallic conduit, in cable trays, as busways, as cablebus, 
in other identified raceways, or as open runs of metal-clad 
cable suitable for the use and purpose. In locations accessible 
to qualified persons only, open runs of Type MV cables, 
bare conductors, and bare busbars shall also be permitted. 
Busbars shall be permitted to be either copper or aluminum. 

300-39. Braid-Covered Insulated Conductors — Open 
Installation. Open runs of braid-covered insulated con- 
ductors shall have a flame-retardant braid. If the conductors 
used do not have this protection, a flame-retardant saturant 
shall be applied to the braid covering after installation. This 
treated braid covering shall be stripped back a safe distance 
at conductor terminals, according to the operating voltage. 
This distance shall not be less than 1 in. (25.4 mm) for each 
kilovolt of the conductor-to-ground voltage of the circuit, 
where practicable. 

300-40. Insulation Shielding. Metallic and semiconduct- 
ing insulation shielding components of shielded cables shall 
be removed for a distance dependent on the circuit voltage 
and insulation. Stress reduction means shall be provided at 
all terminations of factory-applied shielding. 

Metallic shielding components such as tapes, wires, or 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-114 



ARTICLE 300 — WIRING METHODS 



braids, or combinations thereof, and their associated con- 
ducting or semiconducting components shall be grounded. 

300-42. Moisture or Mechanical Protection for Metal- 
Sheathed Cables. Where cable conductors emerge from a 
metal sheath and where protection against moisture or phys- 
ical damage is necessary, the insulation of the conductors 
shall be protected by a cable sheath terminating device. 

300-50. Underground Installations. 

(a) General. Underground conductors shall be identified 
for the voltage and conditions under which they are installed. 
Direct burial cables shall comply with the provisions of 
Section 310-7. Underground cables shall be installed in ac- 
cordance with (1) or (2), and the installation shall meet the 
depth requirements of Table 300-50. 

(1) Shielded Cables and Nonshielded Cables in Metal- 
Sheathed Cable Assemblies. Underground cables, includ- 
ing nonshielded, Type MC and moisture-impervious metal 
sheath cables shall have those sheaths grounded through an 
effective grounding path meeting the requirements of Section 
250-2(d). They shall be direct buried or installed in raceways 
identified for the use. 

(2) Other Nonshielded Cables. Other nonshielded ca- 
bles not covered in (1) shall be installed in rigid metal 
conduit, intermediate metal conduit, or rigid nonmetallic 
conduit encased in not less than 3 in. (76 mm) of concrete. 

(b) Protection from Damage. Conductors emerging from 
the ground shall be enclosed in listed raceways. Raceways 
installed on poles shall be of rigid metal conduit, inter- 
mediate metal conduit, PVC Schedule 80, or equivalent, 
extending from the minimum cover depth specified in Table 
300-50 to a point 8 ft (2.44 m) above finished grade. Conduc- 
tors entering a building shall be protected by an approved 
enclosure or raceway from the minimum cover depth to the 
point of entrance. Where direct-buried conductors, raceways, 
or cables are subject to movement by settlement or frost, 
they shall be installed to prevent damage to the enclosed 
conductors or to the equipment connected to the raceways. 
Metallic enclosures shall be grounded. 

(c) Splices. Direct burial cables shall be permitted to be 
spliced or tapped without the use of splice boxes, provided 
they are installed using materials suitable for the application. 
The taps and splices shall be watertight and protected from 
mechanical damage. Where cables are shielded, the shielding 
shall be continuous across the splice or tap. 

Exception: At splices of an engineered cabling system, me- 
tallic shields of direct-buried single-conductor cables with 
maintained spacing between phases shall be permitted to 
be interrupted and overlapped. Where shields are inter- 



Table 300-50. Minimum Cover Requirements {Cover is defined 
as the shortest distance in inches measured between a point on 
the top surface of any direct-buried conductor, cable, conduit, 
or other raceway and the top surface of finished grade, concrete, 
or similar cover.) 



• 







Rigid 


Rigid Metal 






Nonmetallic 


Conduit and 




Direct- 


Conduit 


Intermediate 


Circuit 


Buried 


Approved for 


Metal 


Voltage 


Cables 


Direct Burial* 


Conduit 


Over 600 V 








through 22 kV 


30 


18 


6 


Over 22 kV 








through 40 kV 


36 


24 


6 


Over 40 kV 


42 


30 


6 



Note: For SI units, 1 in. = 25.4 mm. 

*Listed by a qualified testing agency as suitable for direct burial without 
encasement. All other nonmetallic systems shall require 2 in. (50.8 mm) 
of concrete or equivalent above conduit in addition to above depth. 



rupted and overlapped, each shield section shall be 
grounded at one point. 

(d) Backfill. Backfill containing large rocks, paving mate- 
rials, cinders, large or sharply angular substances, or corro- 
sive materials shall not be placed in an excavation where 
materials can damage raceways, cables, or other substruc- 
tures, or prevent adequate compaction of fill, or contribute 
to corrosion of raceways, cables, or other substructures. 

Protection in the form of granular or selected material or 
suitable sleeves shall be provided to prevent physical damage 
to the raceway or cable. 

(e) Raceway Seal. Where a raceway enters from an under- 
ground system, the end within the building shall be sealed 
with an identified compound so as to prevent the entrance 
of moisture or gases, or it shall be so arranged to prevent 
moisture from contacting live parts. 

Exception No. 1: Areas subject to vehicular traffic, such as 
thoroughfares or commercial parking areas, shall have a 
minimum cover of 24 in. (610 mm). 

Exception No. 2: The minimum cover requirements for other 
than rigid metal conduit and intermediate metal conduit 
shall be permitted to be reduced 6 in. (152 mm) for each 2 in. 
(50.8 mm) of concrete or equivalent protection placed in 
the trench over the underground installation. 

Exception No. 3: The minimum cover requirements shall 
not apply to conduits or other raceways that are located 
under a building or exterior concrete slab not less than 4 in. 
(102 mm) in thickness and extending not less than 6 in. 
(152 mm) beyond the underground installation. A warning 
ribbon or other effective means suitable for the conditions 
shall be placed above the underground installation. 



• 



1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 305 — TEMPORARY WIRING 



70-115 



Exception No. 4: Lesser depths shall be permitted where 
cables and conductors rise for terminations or splices or 
where access is otherwise required. 

Exception No. 5: In airport runways, including adjacent 
defined areas where trespass is prohibited, cable shall be 
permitted to be buried not less than 18 in. (457 mm) deep 
and without raceways, concrete enclosement, or equivalent. 

Exception No. 6: Raceways installed in solid rock shall be 
permitted to be buried at lesser depth where covered by 2 in. 
(50.8 mm) of concrete, which shall be permitted to extend 
to the rock surface. 

Article 305 — Temporary Wiring 

305-1. Scope. The provisions of this article apply to tem- 
porary electrical power and lighting wiring methods that 
may be of a class less than would be required for a permanent 
installation. 

305-2. All Wiring Installations. 

(a) Other Articles. Except as specifically modified in this 
article, all other requirements of this Code for permanent 
wiring shall apply to temporary wiring installations. 

(b) Approval. Temporary wiring methods shall be accept- 
able only if approved based on the. conditions of use and 
any special requirements of the temporary installation. 

305-3. Time Constraints. 

(a) During the Period of Construction. Temporary elec- 
trical power and lighting installations shall be permitted 
during the period of construction, remodeling, maintenance, 
repair, or demolition of buildings, structures, equipment, or 
similar activities. 

(b) 90 Days. Temporary electrical power and lighting in- 
stallations shall be permitted for a period not to exceed 90 
days for Christmas decorative lighting and similar purposes. 

(c) Emergencies and Tests. Temporary electrical power 
and lighting installations shall be permitted during emergen- 
cies and for tests, experiments, and developmental work. 

(d) Removal. Temporary wiring shall be removed imme- 
diately upon completion of construction or purpose for which 
the wiring was installed. 

305-4. General. 

(a) Services. Services shall be installed in conformance 
with Article 230. 

(b) Feeders. Feeders shall be protected as provided in Arti- 
cle 240. They shall originate in an approved distribution 



center. Conductors shall be permitted within cable assem- 
blies, or within cords or cables of a type identified in Table 
400-4 for hard usage or extra-hard usage. For the purpose 
of this section, Type NM and Type NMC cables shall be 
permitted to be used in any dwelling, building, or structure 
without any height limitation. 

Exception: Single insulated conductors shall be permitted 
where installed for the purpose(s) specified in Section 305- 
3(c), where accessible only to qualified persons. 

(c) Branch Circuits. All branch circuits shall originate in 
an approved power outlet or panelboard. Conductors shall be 
permitted within cable assemblies, or within multiconductor 
cord or cable of a type identified in Table 400-4 for hard 
usage or extra-hard usage. All conductors shall be protected 
as provided in Article 240. For the purposes of this section, 
Type NM and Type NMC cables shall be permitted to be 
used in any dwelling, building, or structure without any 
height limitation. 

Branch circuits installed for the purposes specified in 
Sections 305-3(b) or (c) shall be permitted to be run as 
single insulated conductors. Where the wiring is installed 
in accordance with Section 305-3(b), the voltage to ground 
shall not exceed 150 volts, the wiring shall not be subject 
to physical damage, and the conductors shall be supported 
on insulators at intervals of not more than 10 ft (3.05 m); 
or, for festoon lighting, the conductors shall be arranged so 
that excessive strain is not transmitted to the landholders. 

(d) Receptacles. All receptacles shall be of the grounding 
type. Unless installed in a continuous grounded metal race- 
way or metal-covered cable, all branch circuits shall contain 
a separate equipment grounding conductor, and all recepta- 
cles shall be electrically connected to the equipment ground- 
ing conductors. Receptacles on construction sites shall not 
be installed on branch circuits that supply temporary light- 
ing. Receptacles shall not be connected to the same un- 
grounded conductor of multiwire circuits that supply 
temporary lighting. 

(e) Disconnecting Means. Suitable disconnecting switches 
or plug connectors shall be installed to permit the discon- 
nection of all ungrounded conductors of each temporary 
circuit. Multiwire branch circuits shall be provided with a 
means to disconnect simultaneously all ungrounded con- 
ductors at the power outlet or panelboard where the branch 
circuit originated. Approved handle ties shall be permitted. 

(f) Lamp Protection. All lamps for general illumination 
shall be protected from accidental contact or breakage by a 
suitable fixture or lampholder with a guard. 

Brass shell, paper-lined sockets, or other metal-cased 
sockets shall not be used unless the shell is grounded. 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-116 



ARTICLE 310 — CONDUCTORS FOR GENERAL WIRING 



(g) Splices. On construction sites, a box shall not be re- 
quired for splices or junction connections where the circuit 
conductors are multiconductor cord or cable assemblies. 
See Sections 110-14(b) and 400-9. A box, conduit body, or 
terminal fitting having a separately bushed hole for each 
conductor shall be used wherever a change is made to a 
conduit or tubing system or a metal-sheathed cable system. 

(h) Protection from Accidental Damage. Flexible cords 
and cables shall be protected from accidental damage. Sharp 
corners and projections shall be avoided. Where passing 
through doorways or other pinch points, protection shall be 
provided to avoid damage. 

(i) Termination(s) at Devices. Flexible cords and cables 
entering enclosures containing devices requiring termination 
shall be secured to the box with fittings designed for the 
purpose. 

(j) Support. Cable assemblies and flexible cords and ca- 
bles shall be supported in place at intervals that ensure that 
they will be protected from physical damage. Support shall 
be in the form of staples, cable ties, straps, or similar type 
fittings installed so as not to cause damage. 

305-6. Ground-Fault Protection for Personnel. Ground- 
fault protection for personnel for all temporary wiring instal- 
lations shall be provided to comply with (a) and (b). This 
section shall apply only to temporary wiring installations 
used to supply temporary power to equipment used by per- 
sonnel during construction, remodeling, maintenance, repair, 
or demolition of buildings, structures, equipment, or similar 
activities. 

(a) Receptacle Outlets. All 125-volt, single-phase, 15-, 
20-, and 30-ampere receptacle outlets that are not a part of 
the permanent wiring of the building or structure and that are 
in use by personnel shall have ground-fault circuit interrupter 
protection for personnel. If a receptacle(s) is installed or 
exists as part of the permanent wiring of the building or 
structure and is used for temporary electric power, ground- 
fault circuit-interrupter protection for personnel shall be 
provided. For the purposes of this section, cord sets or de- 
vices incorporating listed ground-fault circuit interrupter 
protection for personnel identified for portable use shall be 
permitted. 

Exception No. 1: Receptacles on a 2-wire, single-phase por- 
table or vehicle-mounted generator rated not more than 5 kW, 
where the circuit conductors of the generator are insulated 
from the generator frame and all other grounded sur- 
faces, shall be permitted without ground-fault protection for 
personnel. 

Exception No. 2: In industrial establishments only, where 
conditions of maintenance and supervision ensure that only 



qualified personnel are involved, an assured equipment 
grounding conductor program as specified in Section 305- 
6(b)(2) shall be permitted to be utilized for all receptacle 
outlets. 

(b) Use of Other Outlets. Receptacles other than 125-volt, 
single-phase, 15-, 20-, and 30-ampere receptacles shall have 
protection in accordance with (1) or, the assured equipment 
grounding conductor program in accordance with (2). 

( 1 ) Ground-fault circuit interrupter protection for personnel . 

(2) A written assured equipment grounding conductor prd- 
gram continuously enforced at the site by one or more 
designated persons to ensure that equipment grounding 
conductors for all cord sets, receptacles that are not a 
part of the permanent wiring of the building or structure, 
and equipment connected by cord and plug are installed 
and maintained in accordance with the applicable 
requirements of Sections 210-7(c), 250-114, 250-138, 
and 305-4(d). 

(a) The following tests shall be performed on all cord 
sets, receptacles that are not part of the permanent 
wiring of the building or structure, and cord- and 
plug-connected equipment required to be grounded. 

(1) All equipment grounding conductors shall be 
tested for . continuity and shall be electrically 
continuous. 

(2) Each receptacle and attachment plug shall be 
tested for correct attachment of the equipment 
grounding conductor. The equipment grounding 
conductor shall be connected to its proper 
terminal. 

(3) All required tests shall be performed 

(a) Before first use on site; 

(b) When there is evidence of damage, 

(c) Before equipment is returned to service fol- 
lowing any repairs, 

(d) At intervals not exceeding 3 months. 

(b) The tests required in (2)(a) shall be recorded and 
made available to the authority having jurisdiction. 

305-7. Guarding. For wiring over 600 volts, nominal, suit- 
able fencing, barriers, or other effective means shall be pro- 
vided to limit access only to authorized and qualified 
personnel. 

Article 310 — Conductors for General Wiring 

310-1. Scope. This article covers general requirements for 
conductors and their type designations, insulations, mark- 
ings, mechanical strengths, ampacity ratings, and uses. These 



• 



• 



• 



1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 310 — CONDUCTORS FOR GENERAL WIRING 



70-117 



• 



• 



requirements do not apply to conductors that form an integral 
part of equipment, such as motors, motor controllers, and 
similar equipment, or to conductors specifically provided 
for elsewhere in this Code. 

FPN: For flexible cords and cables, see Article 400. For 
fixture wires, see Article 402. 

310-2. Conductors. 

(a) Insulated. Conductors shall be insulated. 

Exception: Where covered or bare conductors are specifi- 
cally permitted elsewhere in this Code. 

FPN: See Section 250-184 for insulation of neutral conduc- 
tors of a solidly grounded high-voltage system. 

(b) Conductor Material. Conductors in this article shall 
be of aluminum, copper-clad aluminum, or Copper unless 
otherwise specified. 

310-3. Stranded Conductors. Where installed in race- 
ways, conductors of size No. 8 and larger shall be stranded. 

Exception: As permitted or required elsewhere in this Code. 

310-4. Conductors in Parallel. Aluminum, copper-clad 
aluminum, or copper conductors of size No. 1/0 and larger, 
comprising each phase, neutral, or grounded circuit conduc- 
tor, shall be permitted to be connected in parallel (electrically 
joined at both ends to form a single conductor). 

Exception No. 1: As permitted in Section 620- 12(a)(1). 

Exception No. 2: Conductors in sizes smaller than No. 1/0 
shall be permitted to be run in parallel to supply control 
power to indicating instruments, contactors, relays, sole- 
noids, and similar control devices provided 

(a) They are contained within the same raceway or cable, 

(b) The ampacity of each individual conductor is sufficient 
to carry the entire load current shared by the parallel 
conductors, and 

(c) The overcurrent protection is such that the ampacity of 
each individual conductor will not be exceeded if one 
or more of the parallel conductors become inadvertently 
disconnected. 

Exception No. 3: Conductors in sizes smaller than No. 1/0 
shall be permitted to be run in parallel for frequencies of 
360 Hz and higher where conditions (a), (b), and (c) of 
Exception No. 2 are met. 

Exception No. 4: Under engineering supervision, grounded 
neutral conductors in sizes No. 2 and larger shall be permit- 
ted to be run in parallel for existing installations. 

FPN: Exception No. 4 can be utilized to alleviate overheat- 
ing of neutral conductors in existing installations due to high 
content of triplen harmonic currents. 



The paralleled conductors in each phase, neutral, or 
grounded circuit conductor shall 



(1) Be the same length, 

(2) Have the same conductor material, 

(3) Be the same size in circular mil area, 

(4) Have the same insulation type, 

(5) Be terminated in the same manner. 



Where run in separate raceways or cables, the raceways 
or cables shall have the same physical characteristics. Con- 
ductors of one phase, neutral, or grounded circuit conductor 
shall not be required to have the same physical characteristics 
as those of another phase, neutral, or grounded circuit con- 
ductor to achieve balance. 

FPN: Differences in inductive reactance and unequal divi- 
sion of current can be minimized by choice of materials, 
methods of construction, and orientation of conductors. 

Where equipment grounding conductors are used with 
conductors in parallel, they shall comply with the require- 
ments of this section except that they shall be sized in accor- 
dance with Section 250-122. 

Where conductors are used in parallel, space in enclosures 
shall be given consideration (see Articles 370 and 373). 

Conductors installed in parallel shall comply with the 
provisions of Section 3 10- 15(b)(2)(a). 



310-5. Minimum Size of Conductors. The minimum size 
of conductors shall be as shown in Table 310-5. 

Exception No. 1: For flexible cords as permitted by Section 
400-12. 

Exception No. 2: For fixture wire as permitted by Section 
410-24, FPN. 

Exception No. 3: For motors rated 1 hp or less as permitted 
by Section 430-22(c). 

Exception No. 4: For cranes and hoists as permitted by 
Section 610-14. 

Exception No. 5: For elevator control and signaling circuits 
as permitted by Section 620-12. 

Exception No. 6: For Class 1, Class 2, and Class 3 circuits 
as permitted by Sections 725-27(a) and 725-51, Exception. 

Exception No. 7: For fire alarm circuits as permitted by 
Sections 760-27 (a), 760-51, Exception, and 760-7 1(b). 

Exception No. 8: For motor-control circuits as permitted 
by Section 430-72. 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-118 



ARTICLE 310 — CONDUCTORS FOR GENERAL WIRING 



Exception No. 9: For control and instrumentation circuits 
as permitted by Section 727-6. 

Table 310-5. Minimum Size of Conductors 





Minimum Conductor Size (AWG) 


Conductor Voltage 
Rating (Volts) 


Copper 


Aluminum or 
Copper-Clad Aluminum 


0-2000 
2001-8000 
8001-15,000 
15,001-28,000 
28,001-35,000 


14 
8 
2 
1 

1/0 


12 
8 
2 
I 

1/0 



310-6. Shielding. Solid dielectric insulated conductors op- 
erated above 2000 volts in permanent installations shall have 
ozone-resistant insulation and shall be shielded. All metallic 
insulation shields shall be grounded through an effective 
grounding path meeting the requirements of Section 250- 
2(d). Shielding shall be for the purpose of confining the 
voltage stresses to the insulation. 

Exception: Nonshielded insulated conductors listed by a 
qualified testing laboratory shall be permitted for use up to 
8000 volts under the following conditions: 

(a) Conductors shall have insulation resistant to electric 
discharge and surface tracking, or the insulated conductors ) 
shall be covered with a material resistant to ozone, electric 
discharge, and surface tracking. 

(b) Where used in wet locations, the insulated conduc- 
tors) shall have an overall nonmetallic jacket or a continu- 
ous metallic sheath. 

(c) Where operated at 5001 to 8000 volts, the insulated 
conductor(s) shall have a nonmetallic jacket over the insu- 
lation. The insulation shall have a specific inductive capacity 
not greater than 3.6, and the jacket shall have a specific 
inductive capacity not greater than 10 and not less than 6. 

(d) Insulation and jacket thicknesses shall be in accor- 
dance with Table 310-63. 



310-7. Direct Burial Conductors. Conductors used for di- 
rect burial applications shall be of a type identified for such 
use. 

Cables rated above 2000 volts shall be shielded. 

Exception: Nonshielded multiconductor cables rated 2001- 
5000 volts shall be permitted if the cable has an overall 
metallic sheath or armor. 



The metallic shield, sheath, or armor shall be grounded 
through an effective grounding path meeting the require- 
ments of Section 250-2(d). 

FPN No. 1: See Section 300-5 for installation requirements 
for conductors rated 600 volts or less. 

FPN No. 2: See Section 300-50 for installation requirements 
for conductors rated over 600 volts. 

310-8. Locations. 

(a) Dry Locations. Insulated conductors and cables used 
in dry locations shall be any of the types identified in this 
Code. 

(b) Dry and Damp Locations. Insulated conductors and 
cables used in dry and damp locations shall be Types FEP, 
FEPB, MTW, PFA, RH, RHH, RHW, RHW-2, SA, THHN, 
THW, THW-2, THHW, THHW-2, THWN, THWN-2, TW, 
XHH, XHHW, XHHW-2, Z, or ZW. 

(c) Wet Locations. Insulated conductors and cables used 
in wet locations shall be 

(1) Moisture-impervious metal-sheathed; 

(2) Types MTW, RHW, RHW-2, TW, THW, THW-2, 
THHW, THHW-2, THWN, THWN-2, XHHW, XHHW- 
2, ZW; or 

(3) Of a type listed for use in wet locations. 



(d) Locations Exposed to Direct Sunlight. Insulated con- 
ductors and cables used where exposed to direct rays of the 
sun shall be of a type listed or marked "sunlight resistant." 

310-9. Corrosive Conditions. Conductors exposed to oils, 
greases, vapors, gases, fumes, liquids, or other substances 
having a deleterious effect on the conductor or insulation 
shall be of a type suitable for the application. 

310-10. Temperature Limitation of Conductors. No con- 
ductor shall be used in such a manner that its operating 
temperature will exceed that designated for the type of insu- 
lated conductor involved. In no case shall conductors be 
associated together in such a way with respect to type of 
circuit, the wiring method employed, or the number of 
conductors that the limiting temperature of any conductor 
is exceeded. 

FPN: The temperature rating of a conductor (see Tables 
310-13 and 310-61) is the maximum temperature, at any 
location along its length, that the conductor can withstand 
over a prolonged time period without serious degradation. 
The allowable ampacity tables, the ampacity tables of Article 
310 and the ampacity tables of Appendix B, the correction 
factors at the bottom of these tables, and the notes to the 
tables provide guidance for coordinating conductor sizes, 



• 



1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 310 — CONDUCTORS FOR GENERAL WIRING 



70-119 



types, allowable ampacities, ampacities, ambient tempera- 
tures, and number of associated conductors. 

The principal determinants of operating temperature are 
as follows: 

(1) Ambient temperature — ambient temperature may vary 
along the conductor length as well as from time to time. 

(2) Heat generated internally in the conductor as the result of 
load current flow, including fundamental and harmonic 
currents. 

(3) The rate at which generated heat dissipates into the 
ambient medium. Thermal insulation that covers or sur- 
rounds conductors will affect the rate of heat dissipation. 

(4) Adjacent load-carrying conductors — adjacent conduc- 
tors have the dual effect of raising the ambient tempera- 
ture and impeding heat dissipation. 

310-11. Marking. 

(a) Required Information. All conductors and cables shall 
be marked to indicate the following information, using the 
applicable method described in (b): 

(1) The maximum rated voltage for which the conductor 
, , was listed 

(2) The proper type letter or letters for the type of wire or 
cable as specified elsewhere in this Code 

(3) The manufacturer's name, trademark, or other distinc- 
tive marking by which the organization responsible for 
the product can be readily identified 

(4) The AWG size or circular mil area 

(5) Cable assemblies where the neutral conductor is smaller 
than the ungrounded conductors shall be so marked 

(b) Method of Marking. 

(1) Surface Marking. The following conductors and 
cables shall be durably marked on the surface. The AWG 
size or circular mil area shall be repeated at intervals not 
exceeding 24 in. (610 mm). All other markings shall be 
repeated at intervals not exceeding 40 in. (1.02 m). 

(a) Single- and multiconductor rubber- and thermoplastic- 
insulated wire and cable 

(b) Nonmetallic-sheathed cable 

(c) Service-entrance cable 

(d) Underground feeder and branch-circuit cable 

(e) Tray cable 

(f) Irrigation cable 

(g) Power-limited tray cable 
(h) Instrumentation tray cable 

(2) Marker Tape. Metal-covered multiconductor cables 
shall employ a marker tape located within the cable and 
running for its complete length. 

Exception No. 1: Mineral-insulated, metal-sheathed cable. 
Exception No. 2: Type AC cable. 



Exception No. 3: The information required in Section 310- 
11(a) shall be permitted to be durably marked on the outer 
nonmetallic covering of Type MC, Type ITC, or Type PLTC 
cables at intervals not exceeding 40 in. (1.02 m). 

Exception No. 4: The information required in Section 310- 
11(a) shall be permitted to be durably marked on a nonme- 
tallic covering under the metallic sheath of Type ITC or 
Type PLTC cable at intervals not exceeding 40 in. (1.02 m). 

FPN: Included in the group of metal-covered cables are 
Type'AC cable (Article 333), Type MC cable (Article 334), 
and lead-sheathed cable. 

(3) Tag Marking. The following conductors and cables 
shall be marked by means of a printed tag attached to the 
coil, reel, or carton: 



(a) Mineral-insulated, metal-sheathed cable 

(b) Switchboard wires 

(c) Metal-covered, single-conductor cables 

(d) Conductors that have an outer surface of asbestos 

(e) Type AC cable 

(4) Optional Marking of Wire Size. The information 
required in (a)(4) shall be permitted to be marked on the 
surface of the individual insulated conductors for the follow- 
ing multiconductor cables: 



(a) Type MC cable 

(b) Tray cable ! 

(c) Irrigation cable 

(d) Power-limited tray cable 

(e) Power-limited fire alarm cable 

(f) Instrumentation tray cable 

(c) Suffixes to Designate Number of Conductors. A type 
letter or letters used alone shall indicate a single insulated 
conductor. The letter suffixes shall be indicated as follows: 



D — For two insulated conductors laid parallel within 
an outer nonmetallic covering 

M — For an assembly of two or more insulated conduc- 
tors twisted spirally within an outer nonmetallic covering 

(d) Optional Markings. All conductors and cables con- 
tained in Chapter 3 shall be permitted to be surface marked 
to indicate special characteristics of the cable materials. 

FPN: Examples of these markings include but are not lim- 
ited to "LS" for limited smoke and markings such as "sun- 
light resistant." 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-120 



ARTICLE 310 — CONDUCTORS FOR GENERAL WIRING 



310-12. Conductor Identification. 

(a) Grounded Conductors. Insulated or covered grounded 
conductors shall be identified in accordance with Section 
200-6. 

(b) Equipment Grounding Conductors. Equipment 
grounding conductors shall be in accordance with Section 
250-119. 

(c) Ungrounded Conductors. Conductors that are in- 
tended for use as ungrounded conductors, whether used as 
single conductors or in multiconductor cables, shall be fin- 
ished to be clearly distinguishable from grounded and 
grounding conductors. Ungrounded conductors shall be dis- 
tinguished by colors other than white, natural gray, or green; 
or by a combination of color plus distinguishing marking. 
Distinguishing markings shall also be in a color other than 
white, natural gray, or green, and shall consist of a stripe 
or stripes or a regularly spaced series of identical marks. 
Distinguishing markings shall not conflict in any manner 
with the surface markings required by Section 310-1 1(b)(1). 

Exception: As permitted by Section 200-7. 



310-13. Conductor Constructions and Applications. In- 
sulated conductors shall comply with the applicable pro- 
visions of one or more of the following: Tables 310-13, 
310-61, 310-62, 310-63, and 310.-64. 

These conductors shall be permitted for use in any of the 
wiring methods recognized in Chapter 3 and as specified in 
their respective tables. 

FPN: Thermoplastic insulation may stiffen at temperatures 
colder than minus 10°C (plus 14°F). Thermoplastic insula- 
tion may also be deformed at normal temperatures where 
subjected to pressure, such as at points of support. Thermo- 
plastic insulation, where used on dc circuits in wet locations, 
may result in electroendosmosis between conductor and in- 
sulation. 

310-14. Aluminum Conductor Material. Solid aluminum 
conductors No. 8, 10, and 12 shall be made of an AA-8000 
series electrical grade aluminum alloy conductor material. 
Stranded aluminum conductors No. 8 through 1000 kcmil 
marked as Type XHHW, THW, THHW, THWN, THHN, 
service-entrance Type SE Style U and SE Style R shall be 
made of an AA-8000 series electrical grade aluminum alloy 
conductor material. 



• 



• 



• 



Table 310-13. Conductor Application and Insulations 



Thickness of Insulation 



Trade Name Type Letter 



Maximum 

Operating 

Temperature 



Application Provisions 



Insulation 



AWGor 
kcmil 



Mils Outer Covering 1 



Fluorinated ethylene 


FEP 


90°C 


Dry and damp locations 


Fluorinated ethyl- 


14-10 




20 


None 


propylene 


or 
FEPB 


194°F 




ene propylene 


8-2 




30 
























200°C 
392°F 


Dry locations — special 
applications 2 


Fluorinated ethyl- 
ene propylene 


14-8 




14 


Glass braid 
























6-2 




14 


Asbestos or other 
suitable braid 
material 


Mineral insulation 


MI 


90°C 


Dry and wet locations 


Magnesium oxide 


18-16 3 




23 


Copper or alloy 


(metal sheathed) 




194°F 

250°C 
482°F 


For special applications 2 




16-10 

9^4- 

3-500 




36 
50 

55 


steel 


Moisture-, heat-, and 


MTW 


60°C 


Machine tool wiring in wet loca- 


Flame-retardant 




(A) 


(B) 




oil-resistant 




140°F 


tions as permitted in NFPA 79 


moisture-, heat-, 


22-12 


30 


15 


(A) None 


thermoplastic 






(see Article 670) 


and oil-resistant 


10 


30. 


20 








90°C 


Machine tool wiring in dry loca- 


thermoplastic 


8 


45 


30 


(B) Nylon jacket 






194°F 


tions as permitted in NFPA 79 
(see Article 670) 




6 

4-2 

1-4/0 

213-500 

591-1000 


60 
60 
80 
95 
110 


30 
40 
50 
60 
70 


or equivalent 


Paper 




85°C 
185°F 


For underground service con- 
ductors, or by special permis- 
sion 


Paper 








Lead sheath 



'Some insulations do not require an outer covering. 

2 Where design conditions require maximum conductor operating temperatures above 90°C (194°F). 

3 For signaling circuits permitting 300-volt insulation. 



• 



1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 310 — CONDUCTORS FOR GENERAL WIRING 



70-121 



Table 310-13. (Continued) 



Thickness of Insulation 



Trade Name 



Maximum 
Operating 
Type Letter Temperature 



Application Provisions 



Insulation 



AWGor 
kcmil 



Mils Outer Covering 1 



Perfluoroalkoxy 


PFA 


90°C 
194°F 


Dry and damp locations 


Perfluoroalkoxy 


14-10 
8-2 


20 
30 


None 






200°C 


Dry locations — special 




l^t/0 


45 








392°F 


applications 2 










Perfluoroalkoxy 


PFAH 


250°C 


Dry locations only. Only for 


Perfluoroalkoxy 


14-10 


20 


None 






482°F 


leads within apparatus or 
within raceways connected to 
apparatus (Nickel or nickel- 
coated copper only) 




8-2 
1-4/0 


30 

45 




Thermoset 


RH 


75°C 


Dry and damp locations 


Flame-retardant 


14-12 4 


30 


Moisture- 






167°F 




thermoset 


10 


45 


resistant, flame- 


Thermoset 


RHH 


90°C 


Dry and damp locations 




8-2 


60 


retardant, non- 






194°F 






1^1/0 
213-500 
501-1000 
1001-2000 
For 601-2000, see 
Table 310-62 


80 

95 

110 

125 


metallic 
covering 1 


Moisture-resistant 


RHW 5 


75°C 


Dry and wet locations 


Flame-retardant, 


14-10 


45 


Moisture- 


thermoset 




167°F 


Where over 2000 volts insula- 


moisture- 


8-2 


60 


resistant, flame- 








tion, shall be ozone-resistant 


resistant 


1-4/0 


80 


retardant, non- 










thermoset 


213-500 

501-1000 

1001-2000 


95 
110 
125 


metallic 
covering 6 












For 601-2000 volts, see 














Table 310-62 






Moisture-resistant 


RHW-2 


90°C 


Dry and wet locations 


Flame-retardant 


14-10 


45 


Moisture- 


thermoset 




194°F 




moisture- 


8-2 


60 


resistant, flame- 










resistant ther- 


1-4/0 


80 


retardant, non- 










moset 


213-500 

501-1000 

1001-2000 


95 
110 
125 


metallic 
covering 6 












For 601-2000 volts, see 














Table 310-62 






Silicone 


SA 


90°C 


Dry and damp locations 




14-10 


45 


Glass or other suit- 






194°F 






8-2 

1-4/0 

213-500 


60 
80 
95 


able braid mate- 
rial 






200°C 


For special application 2 


Silicone rubber 


501-1000 


110 








392°F 






1001-2000 


125 




Thermoset 


SIS 


90°C 


Switchboard wiring only 


Flame-retardant 


14-10 


30 


None 






194°F 




thermoset 


8-2 
1-4/0 


45 
95 




Thermoplastic and 


TBS 


90°C 


Switchboard wiring only 


Thermoplastic 


14-10 


30 


Flame-retardant, 


fibrous outer braid 




194°F 






8 

6-2 

1-4/0 


45 
60 
80 


nonmetallic 
covering 



'Some insulations do not require an outer covering. 

2 Where design conditions require maximum conductor operating temperatures above 90°C (194 D F). 

4 For size Nos. 14-12, RHH insulation shall be 45 mils thickness. 

5 Listed wire types designated with the suffix "-2," such as RHW-2, shall be permitted to be used at a continuous 

90°C (194°F) operating temperature, wet or dry. 

6 Some rubber insulations do not require an outer covering. 



(continues) 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-122 


ARTICLE 310- 


- CONDUCTORS FOR GENERAL WIRING 


Table 310-13. (Continued) 



Thickness of Insulation 



• 



Trade Name Type Letter 



Maximum 

Operating 

Temperature 



Application Provisions 



Insulation 



AWGor 
kcmil 



'Some insulations do not require an outer covering. 

5 Listed wire types designated with the suffix "-2," such as RHW-2, shall be permitted to be used at a continuous 

90°C (194°F) operating temperature, wet or dry. 

includes integral jacket. 

8 For ampacity limitation, see Section 339-5. 



Mils Outer Covering 1 



Extended polytetra- 


TFE 


250°C 


Dry locations only. Only for 


Extruded poly- 


14-10 


20 


None 


fluoroethylene 




482°F 


leads within apparatus or 


tetrafluoro- 


8-2 


30 










within raceways connected to 


ethylene 


1-470 


45 










apparatus, or as open wiring 
















(Nickel or nickel-coated cop- 
















per only) 










Heat-resistant ther- 


THHN 


90°C 


Dry and damp locations 


Flame-retardant, 


14-12 


15 


Nylon jacket or 


moplastic 




194°F 




heat-resistant 
thermoplastic 


10 

8-6 

4-2 

1-4A) 

250-500 

501-1000 


20 
30 
40 
50 
60 
70 


equivalent 


Moisture- and 


THHW 


,75°C 


Wet location 


Flame-retardant, 


14-10 


30 


None 


heat-resistant 




167°F 




moisture- and 


8 


45 




thermoplastic 




90°C 


Dry location 


heat-resistant 


6-2 


60 








194°F 




thermoplastic 


.1-470 

213-500 
501-1000 


80 

95 

110 




Moisture- and 


THW 5 


75°C 


Dry and wet locations 


Flame-retardant, 


14-10 


30 


None 


heat-resistant 




167°F 




moisture- and 


8 


45 




thermoplastic 




90°C 


Special applications within elec- 


heat-resistant 


6-2 


60 








194°F 


tric discharge lighting equip- 
ment. Limited to 1000 open- 
circuit volts or less (Size 14- 
8 only as permitted in Section 
410-31) 


thermoplastic 


1-4/0 
213-500 
501-1000 
1001-2000 


80 

95 

110 

125 




Moisture- and heat- 


THWN 5 


75°C 


Dry and wet locations 


Flame-retardant, 


14-12 


15 


Nylon jacket or 


resistant thermo- 




167°F 




moisture- and 


10 


20 


equivalent 


plastic 








heat-resistant 
thermoplastic 


8-6 

4-2 

1-4/0 

250-500 

501-1000 


30 
40 
50 
60 
70 




Moisture-resistant 


TW 


60°C 


Dry and wet locations 


Flame-retardant, 


14-10 


30 


None 


thermoplastic 




140°F 




moisture- 
resistant 
thermoplastic 


8 

6-2 

1-4/0 

213-500 

501-1000 

1001-2000 


45 
60 
80 
95 
110 
125 




Underground feeder 


UF 


60°C 


See Article 339 


Moisture-resistant 


14-10 


60 7 


Integral with 


and branch-circuit 




140°F 






8-2 


80 7 


insulation 


cable — single 










1-470- 


95 7 




















(For Type UF cable 


75°C 


Moisture- and 




employing more 




167°F 8 




heat-resistant 








than one conduc- 
















tor, see Article 






t 










339) 

















• 



• 



1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 310 — CONDUCTORS FOR GENERAL WIRING 



70-123 



Table 310-13. (Continued) 



Thickness of Insulation 



Trade Name Type Letter 



Maximum 

Operating 

Temperature 



Application Provisions 



Insulation 



AWGor 
kcmil 



Mils Outer Covering 1 



Underground ser- 


USE 5 


75°C 


See Article 338 


Heat- and 


14-10 


45 


Moisture-resistant 


vice-entrance 




167°F 




moisture- 


8-2 


60 


nonmetallic 


cable — single 








resistant 


1-4/0 


80 


covering [see 


conductor (For 










213-500 


95 9 


Section 


Type USE cable 










501-1000 


110 


338-l(b)] 


employing more 










1001-2000 


125 




than one conduc- 
















tor, see Article 
















338) 
















Thermoset 


XHH 


90°C 


Dry and damp locations 


Flame-retardant 


14-10 


i 30 


None 






194°F 




thermoset 


8-2 

1-4/0 

213-500 

501-1000 

1001-2000 


45 
55 
65 
80 
95 




Moisture-resistant 


XHHW 5 


90°C 


Dry and damp locations 


Flame-retardant, 


14-10 


30 


None 


thermoset 




194°F 




moisture- 


8-2 


45 








75°C 


Wet locations 


resistant 


1-4/0 


55 








167°F 




thermoset 


213-500 

501^1000 

1001-2000 


65 
80 
95 




Moisture-resistant 


XHHW-2 


90°C 


Dry and wet locations 


Flame-retardant, 


14-10 


30 


None 


thermoset 




194°F 




moisture- 
resistant 
thermoset 


8-2 

1-4/0 

213-500 

501-1000 

1001-2000 


45 
55 
65 
80 
95 




Modified ethylene 


Z 


90°C 


Dry and damp locations 


Modified 


14-12 


15 


None 


tetrafluoro- 




194°F 




ethylene- 


10 


20 




ethylene. 




150°C 


Dry locations — special 


tetrafluoro- 


8^1 


25 








302°F 


applications 2 


ethylene 


3-1 
l/(M/0 


35 
45 




Modified ethylene 


zw 5 


75°C 


Wet locations 


Modified 


14-10 


30 


None 


tetrafluoro- 




167°F 




ethylene 


8-2 


45 




ethylene 




90°C 
194°F 
150°C 
302°F 


Dry and damp locations 

Dry locations — special 
applications 2 


tetrafluoro- 
ethylene 









Some insulations do not require an outer covering. 

2 Where design conditions require maximum conductor operating temperatures above 90°C (194°F). 
5 Listed wire types designated with the suffix "-2," such as RHW-2, shall be permitted to be used at a continuous 
90°C (194°F) operating temperature, wet or dry. 

9 Insulation thickness shall be permitted to be 80 mils for listed Type USE conductors that have been subjected 
to special investigations. The nonmetallic covering over individual rubber-covered conductors of aluminum-sheathed 
cable and of lead-sheathed or multiconductor cable shall not be required to be flame retardant. For Type MC 
cable, see Section 334-20. For nonmetallic-sheathed cable, see Section 336-30. For Type UF cable, see Section 
339-1. 



310-15. Ampacities for Conductors Rated 0-2000 Volts. 

(a) General. 

(1) Tables or Engineering Supervision. Ampacities for 
conductors shall be permitted to be determined by tables or 
under engineering supervision, as provided in (b) and (c). 



FPN No. 1 : Ampacities provided by this section do not take 
voltage drop into consideration. See Section 210-19(a), FPN 
No. 4, for branch circuits and Section 215-2(d), FPN No. 
2, for feeders. 

FPN No. 2: For the allowable ampacities of Type MTW 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-124 



ARTICLE 310 — CONDUCTORS FOR GENERAL WIRING 



wire, see Table 11 in the Electrical Standard for Industrial 
Machinery, NFPA 79-1997. 

(2) Selection of Ampacity. Where more than one cal- 
culated or tabulated ampacity could apply for a given circuit 
length, the lowest value shall be used. 

Exception: Where two different ampacities apply to adjacent 
portions of a circuit, the higher ampacity shall be permitted 
to be used beyond the point of transition, a distance equal 
to 10 ft (3.05 m) or 10 percent of the circuit length figured 
at the higher ampacity, Whichever is less. 

FPN: See Section 1 10- 14(c) for conductor temperature lim- 
itations due to termination provisions. 

(b) Tables. Ampacities for conductors rated to 2000 volts 
shall be as specified in the Allowable Ampacity Tables 310- 
16 through 310-19 and Ampacity Tables 310-20 and 
310-21 as modified by (1) through (7). 

FPN: Tables 310-16 through 310-19 are application tables 
for use in determining conductor sizes on loads calculated 
in accordance with Article 220. Allowable ampacities result 
from consideration of one or more of the following: 

(1) Temperature compatibility with connected equipment, 
especially at the connection points. 

(2) Coordination with circuit and system overcurrent protec- 
tion. 

(3) Compliance with the requirements of product listings 
or certifications. See Section 110-3(b). 

(4) Preservation of the safety benefits of established industry 
practices and standardized procedures. 



(1) General. For explanation of type letters used in ta- 
bles and for recognized sizes of conductors for the various 
conductor insulations, see Section 310-13. For installation 
requirements, see Sections 310-1 through 310-10 and the 
various articles of this Code. For flexible cords, see Tables 
400-4, 400-5(A), and 400-5(B). 

(2) Adjustment Factors. 

(a) More than Three Current-Carrying Conductors in a 
Raceway or Cable. Where the number of current-carrying 
conductors in a raceway or cable exceeds three, or where 
single conductors or multiconductor cables are stacked or 
bundled longer than 24 in. (610 mm) without maintaining 
spacing and are not installed in raceways, the allowable 
ampacity of each conductor shall be reduced as shown in 
Table 3 10- 15(b)(2)(a). 

FPN: See Appendix B, Table B-310-1 1, for adjustment fac- 
tors for more than three current-carrying conductors in a 
raceway or cable with load diversity. 

Exception No. 1: Where conductors of different systems, as 
provided in Section 300-3, are installed in a common race- 
way or cable, the derating factors shown in Table 310- 



Table 310-15(b)(2)(a). Adjustment Factors for More than 
Three Current-Carrying Conductors in a Raceway or 
Cable 



Number of Current- 
Carrying Conductors 



Percent of Values in 

Tables 310-16 through 310-19 

as Adjusted for Ambient 

Temperature if Necessary 



4-6 

7-9 

10-20 

21-30 

31^0 

41 and above 



80 
70 
50 
45 
40 
35 



15(b)(2)(a) shall apply to the number of power and lighting 
conductors only (Articles 210, 215, 220, and 230). 

Exception No. 2: For conductors installed in cable trays, 
the provisions of Section 318-11 shall apply. 

Exception No. 3: Derating factors shall not apply to con- 
ductors in nipples having a length not exceeding 24 in. 
(610 mm). 

Exception No. 4: Derating factors shall not apply to under- 
ground conductors entering or leaving an outdoor trench if 
those conductors have physical protection in the form of 
rigid metal conduit, intermediate metal conduit, or rigid 
nonmetallic conduit having a length not exceeding 10 ft 
(3.05 m) and the number of conductors does not exceed 
four. 

(b) More than One Conduit, Tube, or Raceway. Spacing 
between conduits, tubing, or raceways shall be maintained. 

(3) Bare or Covered Conductors. Where bare or cov- 
ered conductors are used with insulated conductors, their 
allowable ampacities shall be limited to those permitted for 
the adjacent insulated conductors. 

(4) Neutral Conductor. 

(a) A neutral conductor that carries only the unbalanced 
current from other conductors of the same circuit shall not 
be required to be counted when applying the provisions of 
Section 3 10- 15(b)(2)(a). 

(b) In a 3-wire circuit consisting of two phase wires and 
the neutral of a 4-wire, 3-phase wye-connected system, a 
common conductor carries approximately the same current 
as the line-to-neutral load currents of the other conductors 
and shall be counted when applying the provisions of Section 
310-15(b)(2)(a). 

(c) On a 4-wire, 3-phase wye circuit where/the major 
portion of the load consists of nonlinear loads, harmonic 
currents are present in the neutral conductor; the neutral 
shall therefore be considered a current-carrying conductor. 



• 



• 



• 



• 



• 



1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 310 — CONDUCTORS FOR GENERAL WIRING 



70-125 



(5) Grounding or Bonding Conductor. A grounding 
or bonding conductor shall not be counted when applying 
the provisions of Section 3 10- 15 (b)(2)(a). 

(6) 120/240- Volt, 3- Wire, Single-Phase Dwelling Ser- 
vices and Feeders. For dwelling units, conductors, as listed 
in Table 3 10- 15(b)(6) shall be permitted as 120/240-volt, 3- 
wire, single-phase service-entrance conductors, service lat- 
eral conductors, and feeder conductors that serve as the main 
power feeder to a dwelling unit and are installed in raceway 
or cable with or without an equipment grounding conductor. 
For application of this section, the main power feeder shall 
be the feeder(s) between the main disconnect and the lighting 
and appliance branch-circuit panelboard(s), and the feeder 
conductors to a dwelling unit shall not be required to be 
larger than their service-entrance conductors. The grounded 
conductor shall be permitted to be smaller, than the un- 
grounded conductors, provided the requirements of Sections 
215-2, 220-22, and 230-42 are met. 

Table 310-15(b)(6). Conductor Types and Sizes for 120/240- 
Volt, 3- Wire, Single-Phase Dwelling Services and Feeders. 
Conductor Types RH, RHH, RHW, RHW-2, THHN, THHW, 
TH W, THW-2, THWN, THWN-2, XHHW, XHHW-2, SE, USE, 

USE-2 





Conductor 






(AWG or kcmil) 






Aluminum or 


Service or 




Copper-Clad 


Feeder Rating 


Copper 


Aluminum 


(Amperes) 


4 


2 


100 


3, 


1 


110 


2 


1/0 


125 


1 


2/0 


150 


1/0 


3/0 


175 


2/0 


4/0 


200 


3/0 


250 


225 


4/0 


300 


250 


250 


350 


300 


350 


500 


350 


400 


600 


400 



(7) Mineral-Insulated, Metal-Sheathed Cable. The 

temperature limitations on which the ampacities of mineral- 
insulated, metal-sheathed cable are based shall be deter- 
mined by the insulating materials used in the end seal. 
Termination fittings incorporating unimpregnated, organic, 
insulating materials shall be limited to 90°C (194°F) 
operation. 

(c) Engineering Supervision. Under engineering supervi- 
sion, conductor ampacities shall be permitted to be calculated 
by means of the following general formula: 



/ = 



TC - (TA + DeltaTD) 
RDC(\ + YQRCA 



Where: 

TC = Conductor temperature in degrees Celsius 

(°C) 
TA = Ambient temperature in degrees Celsius (°C) 
Delta TD = Dielectric loss temperature rise 

RDC = dc resistance of conductor at temperature TC 
YC = Component ac resistance resulting from skin 
effect and proximity effect 
RCA = Effective thermal resistance between con- 
ductor and surrounding ambient 

FPN: See Appendix B for examples of formula applications. 
310-60. Conductors Rated 2001 to 35,000 Volts. 

(a) Definitions. 

Electrical Ducts. As used in Article 310, electrical ducts 
shall include any of the electrical conduits recognized in 
Chapter 3 as suitable for use underground; and other race- 
ways round in cross section, listed for underground use, and 
embedded in earth or concrete. 

Thermal Resistivity. As used in this Code, thermal re- 
sistivity refers to the heat transfer capability through a sub- 
stance by conduction. It is the reciprocal of thermal 
conductivity and is designated Rho and expressed in the 
units °C-cm/watt. 

(b) Ampacities of Conductors Rated 2001 to 35,000 Volts. 

Ampacities for solid dielectric-insulated conductors shall be 
permitted to be determined by tables or under engineering 
supervision, as provided in (c) and (d). 

(1) Selection of Ampacity. Where more than one calcu- 
lated or tabulated ampacity could apply for a given circuit 
length, the lowest value shall be used. 

Exception: Where two different ampacities apply to adjacent 
portions of a circuit, the higher ampacity shall be permitted 
to be used beyond the point of transition, a distance equal 
to 10 ft (3.05 m) or 10 percent of the circuit length figured 
at the higher ampacity, whichever is less. 

FPN: See Section 1 10-40 for conductor temperature limita- 
tions due to termination provisions. 

(c) Tables. Ampacities for conductors rated 2001 to 35,000 
volts shall be as specified in the Ampacity Tables 310-67 
through 310-86. Ampacities at ambient temperatures other 
than those shown in the tables shall be determined by the 
formula in (4). 

FPN No. 1: For ampacities calculated in accordance with 
Section 310-60(b), reference IEEE Standard Power Cable 
Ampacity Tables, IEEE 835-1994 (IPCEA Pub. No. P-46- 
426) and the references therein for availability of all factors 
and constants. 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-126 



ARTICLE 310 — CONDUCTORS FOR GENERAL WIRING 



Table 310-16. Allowable Ampacities of Insulated Conductors Rated through 2000 Volts, 60°C 
through 90°C (140°F through 194°F) Not More than Three Current-Carrying Conductors in 
Raceway, Cable, or Earth (Directly Buried), Based on Ambient Temperature of 30°C (86°F) 



Size 


Temperature Rating of Conductor (See Table 310-13) 


Size 




60°C 


75°C 


90°C 


60°C 


75°C ■ 


90°C 






(140°F) 


. (167°F) 


(194°F) 


(140°F) 


(167°F) 


(194°F) 






Types 


Types FEPW, 


Types TBS, SA, 


Types 


Types RH, 


Types TBS, SA, 






TW,UF 


RH, RHW, 


SIS, FEP, FEPB, 


TW,UF 


RHW, 


SIS, THHN, 








THHW, THW, 


MI, RHH, RHW- 




THHW, 


THHW, THW-2, 




AWGor 




THWN, 


2, THHN, THHW, 




THW, 


THWN-2, RHH, 


AWGor 


kcmil 




XHHW, USE, 


THW-2, THWN- 




THWN, 


RHW-2, USE-2, 


kcmil 






ZW 


2, USE-2, XHH, 
XHHW, XHHW- 
2, ZW-2 


- 


XHHW, USE 


XHH, XHHW, 
XHHW-2, ZW-2 






COPPER 


ALUMINUM OR COPPER-CLAD ALUMINUM 




18 






14 










16 


— 


— 


18 


— 


— 


— 


— 


14* 


20 


20 


25 


— 


— 


— 


— 


12* 


25 


25 


30 


20 


20 


25 


12* 


10* 


30 


35 


40 


25 


30 


35 


10* 


8 


40 


50 


55 


30 


40 


45 


8 


6 


55 


65 


75 


40 


50 


60 


6 


4 


70 


85 


95 


55 


65 


75 


4 


3 


85 


100 


110 


65 


75 


85 


3 


2 


95 


115 


130 


75 


90 


100 


2 


1 


110 


130 


150 


85 


100 


115 


1 


1/0 


125 


150 


170 


100 


120 


135 


1/0 


2/0 


145 


■ 175 


195 


115 


135 


150 


2/0 


3/0 


165 


200 


225 


130 


155 


175 


3/0 


4/0 


195 


230 


260 


150 


180 


205 


4/0 


250 


215 


255 


290 


170 


205 


230 


250 


300 


240 


285 


320 


190 


230 


255 


300 


350 


260 


310 


350 


210 


. 250 


280 


350 


400 


280 


335 


380 


225 


270 


305 


400 


500 


320 


380 


430 


260 


310 


350 


500 ' 


600 


355 


420 


475 


285 


340 


385 


600 


700 


385 


460 


520 


3 id 


375 


420 


700 


. 750 


400 


475 


535 


320 


385 


435 


750 


800 


410 


490 


555 


330 


395 


450 


800 


900 


435 


520 


585 


355 


425 


480 


900 


1000 


455 


545 


615 


375 


445 


500 


1000 


1250 


495 


590 


665 


405 


485 


■ 545 


1250 


1500 


520 


625 


705 


435 


520 


585 


1500 


1750 


545 


650 


735 


455 


545 


615 


1750 


2000 


560 


665 


750 


470 


560 


630 


2000 



CORRECTION FACTORS 



Ambient 


For ambient temperatures other than 30°C (86°F), multiply the allowable ampacities shown above by the 


Ambient 


Temp. (°C) 


appropriate factor shown below. 


Temp. (°F) 


21-25 


1.08 


1.05 


1.04 


1.08 


1.05 


1.04 


70-77 


26-30 


1.00 


1.00 


1.00 


1.00 


1.00 


1.00 


78-86 


31-35 


0.91 


0.94 


0.96 


0.91 


0.94 


0.96 


87-95 


36-40 


0.82 


0.88 


0.91 


■0.82 


0.88 


0.91 


96-104 


41—45 


0.71 


0.82 


0.87 


0.71 


0.82 


0.87 


105-113 


46-50 


0.58 


0.75 


0.82 


0.58 


0.75 


0.82 


114-122 


51-55 


0.41 


0.67 


0.76 


0.41 


0.67 


0.76 


123-131 


56-60 


— 


0.58- 


0.71 


— 


0.58 


0.71 


132-140 


61-70 


— 


0.33 


0.58 


— 


0.33 


0.58 


141-158 


71-80 


— 


— 


0.41 


— 


— 


0.41 


159-176 



• 



*See Section 240-3. 



1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 310 — CONDUCTORS FOR GENERAL WIRING 



70-127 



Table 310-17. Allowable Ampacities of Single-Insulated Conductors Rated Through 2000 Volts 
in Free Air, Based on Ambient Air Temperature of 30°C (86°F) 



Size 


Temperature Rating of Conductor (See Table 310-13) 


Size 




60°C 


75°C 


90°C 


60°C 


75°C 


90°C 






(140°F) 


(167°F) 


(194°F) 


(140°F) 


(167°F) 


(194°F) 






Types 


Types FEPW, 


Types TBS, SA, 


Types 


Types RH, 


Types TBS, SA, 






TW,UF 


RH, RHW, 


SIS, FEP, FEPB, 


TW, UF 


RHW, THHW, 


SIS, THHN, 








THHW, THW, 


MI, RHH, RHW-2, 




THW, THWN, 


THHW, THW-2, 




AWGor 




THWN, 


THHN, THHW, 




XHHW 


THWN-2, RHH, 


AWGor 


kcmil 




XHHW, ZW 


THW-2, THWN-2, 
USE-2, XHH, 
XHHW, XHHW-2, 
ZW-2 






RHW-2, USE-2, 
XHH, XHHW, 
XHHW-2, ZW-2 


kcmil 




COPPER 


ALUMINUM OR COPPER-CLAD ALUMINUM 




18 
16 
14* 


— 


— 


18 

24 
35 


— 


— 


— 


— 


' 25 


30 














12* 


30 


35 


40 


25 , 


30 


35 


12* 


10* 


40 


50 


55 


35 


40 


40 


10* 


8 


60 


70 


80 


45. 


55 


60 


8 


6 


80 


95 


105 


60 


75 


80 


6 


4 


105 


125 


140 


80 


100 


110 


4 


3 


120 


145 


165 


95 


115 


130 


3 


2 


140 


170 


190 


110 


135 


150 


2 


1 


165 


195 


220 


130 


155 


175 


1 


1/0 


195 


230 


260 


150 


180 


205 


1/0 


2/0 


225 


265 


300 


175 


210 


235 


2/0 


3/0 


260 


310 


350 


200 


240 


275 


3/0 


4/0 


300 


360 


405 


235 


280 


315 


4/0 


250 


340 


405 


455 


265 


315 


355 


250 


300 


375 


455 


505 


290 


350 


395 


300 


350 


420 


505 


570 


330 


395 


445 


350 


400 


455 


545 


615 


355 


425 


480 


400 


500 


515 


620 


700 


405 


485 


545 


500 


600 


575 


690 


780 


455 


540 


615 


600 


700 


630 


755 


855 


500 


595 


675 


700 


750 


655 


785 


885 


515 


620 


700 


750 


800 


680 


815 


920 


535 


645 


725 


800 


900 


730 


870 


985 


580 


700 


785 


900 


1000 


780 


935 


1055 


625 


750 


845 


1000 


1250 


890 


1065 


1200 


710 


855 


960 


1250 


1500 


980 


1175 


1325 


795 


950 


1075 


1500 


1750 


1070 


1280 


1445 


875 


1050 


1185 


1750 


2000 


1155 


1385 


1560 


960 


1150 


1335 


2000 



CORRECTION FACTORS 



Ambient 


For ambient temperatures other than 30°C (86°F), multiply the allowable ampacities shown above by the 


Ambient 


Temp. (°C) 


appropriate factor shown below. 


Temp. (°F) 


21-25 


1.08 


1.05 


1.04 


1.08 


1.05 


1.04 


70-77 


26-30 


1.00 


1.00 


1.00 


1.00 


1.00 


1.00 


78-86 


31-35 


0.91 


0.94 


0.96 


0.91 


0.94 


0.96 


87-95 


36^10 


0.82 


0.88 


0.91 


0.82 


0.88 


0.91 


96-104 


41^5 


0.71 


0.82 


0.87 


0.71 


0.82 


0.87 


105-113 


46-50 


0.58 


0.75 


0.82 


0.58 


0.75 


0.82 


114-122 


51-55 


0.41 


0.67 


0.76 


0.41 


0.67 


0.76 


123-131 


56-60 


— ' 


0.58 


0.71 


— 


0.58 


0.71 


132-140 


61-70 


— 


0.33 


0.58 


-r- 


0.33 


0.58 


141-158 


71-80 


— 


— 


0.41 





— 


0.41 


159-176 



I *See Section 240-3. 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-128 



ARTICLE 310 — CONDUCTORS FOR GENERAL WIRING 



Table 310-18. Allowable Ampacities of Three Single-Insulated Conductors, Rated Through 
2000 Volts, 150°C Through 250°C (302°F Through 482°F), in Raceway or Cable, Based on Ambient 
Air Temperature of 40°C (104°F) 



Size 


Temperature Rating of Conductor (See Table 310-13) 


Size 




150°C 


200°C 


250°C 


150°C 






(302°F) 


(392°F) 


(482°F) 


(302°F) 






TypeZ 


Types FEP, 


Types PFAH, TFE 


TypeZ 




AWG or kcmil 




FEPB, PFA 






AWG or kcmil 








NICKEL OR 


ALUMINUM OR 










NICKEL-COATED 


COPPER-CLAD 






COPPER 


COPPER 


ALUMINUM 




14 


34 


36 


39 




14 


12 


43 


45 


54 


30 


12 


10 


55 


60 


73 


44 


10 


8 


76 


83 


93 


57 


8 


6 


96 


110 


117 


75 


6 


4 


120 


125 


148 


94 


4 


3 


143 


152 


166 


109 


3 


2 


160 


171 


191 


124 


2 


1 


186 


197 


215 


145 


1 


1/0 


215 


229 


244 


169 


1/0 


2/0 


251 


260 


273 


198 


2/0 


3/0 


288 


297 


308 


227 


3/0 


4/0 


332 


346 


361 


260 


4/0 



CORRECTION FACTORS 



• 



• 







For ambient temperatures other than 40°C (104°F), 










multiply the allowable ampacities shown above by 






Ambient Temp. (°C) 




the appropriate factor shown below. 




Ambient Temp. (°F) 


41-50 


0.95 


0.97 


0.98 




0.95 


105-122 


51-60 


0.90 


0.94 


0.95 




0.90 


123-140 


61-70 


0.85 


0.90 


0.93 




0.85 


141-158 


71-80 


0.80 


0.87 


0.90 




0.80 


159-176 


81-90 


0.74 


0.83 


0.87 




0.74 


177-194 


91-100 


0.67 


0.79 


0.85 




0.67 


195-212 


101-120 


0.52 


0.71 


0.79 




0.52 


213-248 


121-140 


0.30 


0.61 


0.72 




0.30 


249-284 - 


141-160 


— 


0.50 


0.65 




. — 


285-320 


161-180 


— ■ 


0.35 


0.58 




— 


321-356 


181-200 


— 


— 


0.49 




— 


357-392 


• 201-225 


— 


— 


0.35 




— 


393-437 



FPN No. 2: Ampacities provided by this section do not take 
voltage drop into consideration. See Section 210-19(a), FPN 
No. 4, for branch circuits and Section 215-2(d), FPN No. 
2, for feeders. 



(1) Grounded Shields. Ampacities shown in Tables 
310-69, 310-70, 310-81, and 310-82 are for cable with 
shields grounded at one point only. Where shields are 
grounded at more than one point, ampacities shall be adjusted 
to take into consideration the heating due to shield currents. 



(2) Burial Depth of Underground Circuits. Where the 
burial depth of direct burial or electrical duct bank circuits 
is modified from the values shown in a figure or table, 
ampacities shall be permitted to be modified as indicated in 
(a) and (b). 

(a) Where burial depths are increased in part(s) of an 
electrical duct run, no decrease in ampacity of the conductors 
is needed, provided the total length of parts of the duct run 
increased in depth is less than 25 percent of the total run 
length. 



1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 310 — CONDUCTORS FOR GENERAL WIRING 



70-129 



Table 310-19. Allowable Ampacities of Single-Insulated Conductors, Rated Through 2000 
Volts, 150°C Through 250°C (302°F Through 482°F), in Free Air, Based on Ambient Air 
Temperature of 40°C (104°F) 



Size 


Temperature Rating of Conductor (See Table 310-13) 


Size 




150°C 


200°C 


250°C 


150°C 




AWG or 


(302°F) 


(392°F) 


(482°F) 


(302°F) 


AWG or 


kcmil 


TypeZ 


Types FEP, 
FEPB, PFA 


Types PFAH, TFE 


TypeZ 


kcmil 








NICKEL, OR 


ALUMINUM OR 










NICKEL-COATED 


COPPER-CLAD 






COPPER 


COPPER 


ALUMINUM 




14 


46 


54 


59 


_ 


14 


12 


60 


68 


78 


47 


12 


10 


80 


90 


107 


63 


10 


8 


106 


124 


142 


83 


8 


6 


155 


165 


205 


112 


6 


4 


190 


220 


278 


148 


4 


3 


214 


252 


327 


170 


3 


2 


255 


293 


381 


198 


2. 


1 


293 


344 


440 


228 


1 


1/0 


339 


399 


532 


263 


1/0 


2/0 


390 


467 


591 


305 


2/0 


3/0 


451 


546 


708 


351 


3/0 


4/0 


529 


629 


830 


411 


4/0 



CORRECTION FACTORS 







For ambient temperatures other than 40°C (104°F), 






Ambient 




multiply the allowable ampacities shown above by 




Ambient 


Temp. (°C) 




the appropriate factor shown below. 




Temp. (°F) 


41-50 


0.95 


0.97 


0.98 




0.95 


105-122 


51-60 


0.90 


0.94 


0.95 




0.90 


123-140 


61-70 


0.85 


0.90 


0.93 




0.85 


141-158 


71-80 


0.80 


0.87 


0.90 




0.80 


159-176 


81-90 


0.74 


0.83 


0.87 




0.74 


177-194 


91-100 


0.67 


0.79 


0.85 




0.67 


195-212 


101-120 


0.52 


0.71 


0.79 




0.52 


213-248 


121-140 


0.30 


0.61 


0.72 




0.30 


249-284 


141-160 


' — 


0.50 


0.65 




— 


285-320 


161-180 


— 


0.35 


0.58 




— 


321-356 


181-200 


— 


— 


0.49 




. — 


357-392 


201-225 


— 


— 


0.35 




— 


393^37 



(b) Where burial depths are deeper than shown in a spe- 
cific underground ampacity table or figure, an ampacity 
derating factor of 6 percent per increased foot (305 mm) of 
depth for all values of Rho shall be permitted. 

No rating change is needed where the burial depth is 
decreased. 



(3) Electrical Ducts in Figure 310-60. At locations 
where electrical ducts enter equipment enclosures from 
underground, spacing between such ducts, as shown in Fig- 
ure 310-60, shall be permitted to be reduced without requir- 
ing the ampacity of conductors therein to be reduced. 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-130 



ARTICLE 310 — CONDUCTORS FOR GENERAL WIRING 



Table 310-20. Ampacities of Two or Three Single-Insulated 


Conductors, Rated Through 2000 Volts, Supported on a 


Messenger, Based on Ambient Air Temperature of 40°C (104°F) 




Temperature Rating of Conductor 




Size 


(See Table 310-13) 


Size 




75°C 


90°C 


75°C 


90°C 






(167°F) 


(194°F) 


(167°F) 


(194°F) 




Types 


Types 


Types 


Types 






RH, 


THHN, 


RH, 


THHN, 






RHW, 


THHW, 


RHW, 


THHW, 




AWGor 


THHW, 


THW-2, 


THW, 


RHH, 


AWGor 


kcmil 


THW, 


THWN- 


THWN, 


XHHW, 


kcmil 




THWN, 


2, RHH, 


THHW, 


RHW-2, 






XHHW, 


RWH-2, 


XHHW 


XHHW- 






ZW 


USE-2, 
XHHW, 
XHHW- 
2, ZW-2 




2, THW- 

2, 
THWN- 

2, USE-2, 
ZW-2 






ALUMINUM OR 








COPPER-CLAD 






COPPER 


ALUMINUM 




8 


57 


66 


44 


51 


8 


6 


76 


89 


59 


69 


6 


4 


101 


117 


78 


91 


4 


3 


118 


138 


92 


107 


3 


2 


135 


158 


106 


123 


2 


1 


158 


185 


123 


144 


1 


1/0 


183 


214 


143 


167 


1/0 


2/0 


212 


247 


165 


193 


2/0 


3/0 


245 


287 


192 


224 


3/0 


4/0 


287 


335 


224 


262 


4/0 


250 


320 


374 


251 


292 


250 


300 


359 


419 


282 


328 


300 


350 


397 


464 


312 


364 


350 


400 


430 


503 


339 


395 


400 


500 


496 


580 


392 


458 


500 


600 


553 


647 


440 


514 


600 


700 


610 


714 


488 


570 


700 


750 


638 


747 


512 


598 


750 


800 


660 


773 


532 


622 


800 


900 


704 


826 


572 


669 


900 


1000 


748 


879 


612 


716 


1000 




For ambient temperatures other than 40°C 




Ambient 


(104°F), multiply the allowable ampacities 


Ambient 


Temp. 


shown above by the appropriate factor shown 


Temp. 


(°C). 


below. 


(°F) 


21-25 


1.20 


1.14 


1.20 


1.14 


70-77 


26-30 


1.13 


1.10 


1.13 


1.10 


79-86 


31-35 


1.07 


1.05 


1.07 


1.05 


88-95 


36-40 


1.00 


1.00 


1.00 


1.00 


97-104 


41-45 


0.93 


0.95 


0.93 


0.95 


106-113 


46-50 


0.85 


0.89 


0.85 


0.89 


115-122 


51-55 


0.76 


0.84 


0.76 


0.84 


124-131 


56-60 


0.65 


0.77 


0.65 


0.77 


133-140 


61-70 


0.38 


0.63 


0.38 


0.63 


142-158 


71-80 


— 


0.45 


— 


0.45 


160-176 



Table 310-21. Ampacities of Bare Covered Conductors, 
Based on 40°C (104°F) Ambient, 80°C (176°F) Total Conductor 
Temperature, 2 ft/sec (610 mm/sec) Wind Velocity 

Copper Conductors 



Bare 



Covered 



AWGor 




AWGor 




kcmil 


Amperes 


kcmil 


Amperes 


8 


98 


8 


103 


6 


124 


6 


130 


4 


155 


4 


163 


2 


209 


2 


219 



1/0 


282 


1/0 


297 


2/0 


329 


2/0 


344 


3/0 


382 


3/0 


401 


4/0 


444 


4/0 


466 


250 


494 


. 250 


519 


300 


556 


300 


584 


500 


773 


500 


812 


750 


1000 


750 


1050 


1000 


1193 


1000 


1253 


— 


— 


— 


— 



AAC Aluminum Conductors 



8 


76 


8 


80 


6 


96 


6 


101 


4 


121 


4 


127 


2 


163 


2 


171 


1/0 


220 


1/0 


231 


2/0 


255 


2/0 


268 


3/0 


297 


3/0 


312 


4/0 


346 


4/0 


364 


266.8 


403 


266.8 


423 


336.4 


468 


336.4 


492 


397.5 


522 


397.5 


548 


477.0 


588 


477.0 


617 


556.5 


650 


556.5 


682 


636.0 


709 


636.0 


744 


795.0 


819 


795.0 


860 


954.0 


920 


— 


— 


1033.5 


968 


1033.5 


1017 


1272 


1103 


1272 


1201 


1590 


1267 


1590 


1381 


2000 


1454 


2000 


1527 



• 



• 



• 



1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 310 — CONDUCTORS FOR GENERAL WIRING 



70-131 



Table 310-61. Conductor Application and Insulation 







Maximum 








Trade 


Type 


Operating 


Application 




Outer 


Name 


Letter 


Temperature 


Provision 


Insulation 


Covering 


Medium 


MV-90 


90°C 


Dry or wet 


Thermo- 


Jacket, 


voltage 


MV-105* 


105°C 


locations 


plastic or 


sheath, or 


solid 






rated 2001 


thermo- 


armor 


dielectric 






volts and 
higher 


setting 





* Where design conditions require maximum conductor temperatures 
above 90°C. 



Table 310-62. Thickness of Insulation for 601 to 2000- Volt 
Nonshielded Types RHH and RHW, in Mils 



Conductor Size 


Column 


Column 


(AWG or kcmil) 


A 1 


B 2 


14-10 


80 


60 


8 


80 


70 


6-2 


95 


70 


1-2/0 


110 


90 


3/0-4/0 


110 


90 


213-500 


125 


105 


501-1000 


140 


120 



'Column A insulations are limited to natural,. SBR, and butyl rubbers. 
2 Column B insulations are materials such as cross-linked polyethylene, 
ethylene propylene rubber, and composites thereof. 



(4) Ambients Not in Tables. Ampacities at ambient 
temperatures other than those shown in the tables shall be 
determined by means of the following formula: 



h = h 



I TC - TA 2 - Delta TD 
TC - TA l - Delta TD 



Where: 



/j = ampacity from tables at ambient TA { 
I 2 = ampacity at desired ambient TA 2 
TC = conductor temperature in degrees Celsius (°C) 
TA^ = surrounding ambient from tables in degrees 

Celsius (°C) 
TA 2 = desired ambient in degrees Celsius (°C) 
Delta TD = dielectric loss temperature rise 

(d) Engineering Supervision. Under engineering supervi- 
sion, conductor ampacities shall be permitted to be calculated 
by means of the following general formula: 



TC - (TA + Delta TD) 
~ \ RDC (1 + YQRCA 

Where: 

TC = conductor temperature in °C 
TA = ambient temperature in °C 
Delta TD = dielectric loss temperature rise 

RDC = dc resistance of conductor at temperature TC 
YC = component ac resistance resulting from skin 
effect and proximity effect 
RCA = effective thermal resistance between conductor 
and surrounding ambient 

FPN: See Appendix B for examples of formula applica- 
tions. 



Table 310-63. Thickness of Insulation and Jacket for Nonshielded Solid Dielectric Insulated 
Conductors Rated 2001 to 8000 Volts, in Mils 









2001- 


-5000 Volts 


































Dry Locations, Single Conductor 
Without With Jacket 




Wet 


or Dry Locations 


Level We( 


or Dry 


Locations 


Conductor Size 


Single 


Conductor 


Multi- 
conductor* 


Single Conductor 


Multi- 


Jacket 
















conductor* 


(AWG or kcmil) 


Insulation 


Insulation 


Jacket 


Insulation 


Jacket 


Insulation 


Insulation 


Jacket 


Insulation 


8 


110 


90 


30 


125 




80 


90 ' 


180 


80 


180 


6 


110 


90 


30 


125 




80 


90 


180 


80 


180 


4-2 


110 


90 


45 


125 




80 


90 


180 


95 


180 


1-2/0 


110 


90 


45 


125 




80 


90 


180 


95 


180 


3/0-4/0 


110 


90 


65 


125 




95 


90 


180 


110 


180 


213-500 


120 


90 


65 


140 




110 


90 


210 


110 


210 


501-750 


130 


90 


65 


155 




125 


90 


235 


125 


235 


751-1000 


130 


90 


65 


155 




125 


90 


250 


140 


' 250 


*Under a common 


overall covering 


such as a jacket, 


sheath, 


Dr armor. 














NATIONAL ELECTRICAL CODE 


















1999 Edition 



70-132 



ARTICLE 310 — CONDUCTORS FOR GENERAL WIRING 



N c t>". 

'id? 



Detail 1 

11 .5 in. x 11.5 in. 
Electrical duct bank 
One electrical duct 




7.5 in: 



Detail 2 

19 in. x 19 in. 
Electrical duct bank 
Three electrical ducts 

or 



m$- 



7.5 in. 7.5 in. 

27 in. x11.5.in. 
Electrical duct bank 
Three electrical ducts 



/v \ P 



^ • 7.5 in. 



Detail 3 

19 in. x 27 in. 
Electrical duct bank 
Six electrical ducts 




7.5 in. 7.5 in. 



27 in. x 19 in. 
Electrical duct bank 
Six electrical ducts 



Tq 7.5 in. 7.5 in. , 



Detail 4 

27 in. x 27 in. 
Electrical duct bank 
Nine electrical ducts 



• 



• 









■< — 


24 in. 


• 


i 


i 


4 


Detail 5 

Buried 3 

conductor 

cable 




Detail 6 

Buried 3 

conductor 

cables 




7.5 in. 


7.5 in. 




< 


i i 


> 4 


> 


Del 

Bu 
cat 


ail 9 

ied sin 
iles (1 


gle 
circ 


-cot 
;uit) 


lductor 



A 

Detail 7 

Buried triplexed 
cables (1 circuit) 



£ 



24 in. 



1 



•• 



Detail 8 

Buried triplexed 
cables (2 circuits) 



4 >■ 

7.5 in. 


< — »■ 

7.5 in. 


< — 


24 in. 


*■ 


< — *■ 

7.5 in. 


•< — > 

7.5 in. 


• i 


> i 


> 




i 


i i 


> i 



Detail 10 

Buried single-conductor 
cables (2 circuits) 



Legend 



Note 1 : Minimum burial depths to top electrical ducts or cables shall be in 
accordance with Section 300-50. Maximum depth to the top of 
electrical duct banks shall be 30 in. and maximum depth to the top 
of direct buried cables shall be 36 in. 



O 

Note 2: For SI units: 1 in. = 25.4 mm; 1 ft = 0.3048 m. • 

Figure 310-60 Cable installation dimensions for use with Tables 310-77 through 310-86. 



Backfill 

(earth or concrete) 

Electrical duct 

Cable or cables 



• 



Table 310-64. Thickness of Insulation for Shielded Solid Dielectric Insulated Conductors Rated 2001 to 35,000 Volts, in Mils 

5001-8000 Volts 8001-15,000 Volts 15,001-25,000 Volts 25,001-28,000 Volts 28,001-35,000 Volts 

Conductor : 

Size 2001- 100 Percent 133 Percent 100 Percent 133 Percent 100 Percent 133 Percent 100 Percent 133 Percent 100 Percent 133 Percent 
(AWG or 5000 Insulation Insulation Insulation Insulation Insulation Insulation Insulation Insulation Insulation Insulation 



kcmil) Volts Level 



Level 2 



Level 1 



LeveH 



Level 1 



Level 2 



Level 1 



Level 2 



Level 1 



Level 2 



8 


90 


— 


— 


— 


— 


— 


— 


— 


_ 


6-4 


90 


115 


140 


— 


— 


— 


— 


. — 


— 


2 


90 


115 


140 


175 


215 


— 


— 


— 


— 


1 


90 


115 


140 


175 


215 


260 


345 


280 


345 


1/0-2000 


90 


115 


140 


175 


215 


260 


345 


280 


. 345 



345 



420 



'100 Percent Insulation Level. Cables in this category shall be permitted to be applied where the system is provided with relay protection such that 
ground faults will be cleared as rapidly as possible but, in any case, within 1 minute. While these cables are applicable to the great majority of cable 
installations that are on grounded systems, they shall be permitted to be used also on other systems for which the application of cables is acceptable, 
provided the above clearing requirements are met in completely de-energizing the faulted section. 

2 133 Percent Insulation Level. This insulation level corresponds to that formerly designated for grounded systems. Cables in this category shall be 
permitted to be applied in situations where the clearing time requirements of the 100 percent level category cannot be met, and yet there is adequate 
assurance that the faulted section will be de-energized in a time not exceeding 1 hour. Also, they shall be permitted to be used where additional 
insulation strength over the 100 percent level category is desirable. 



• 



1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 310 — CONDUCTORS FOR GENERAL WIRING 



70-133 



Table 310-67. Ampacities of Insulated Single Copper 
Conductor Cables Triplexed in Air Based on Conductor 
Temperatures of 90°C (194°F) and 105°C (221°F) and 
Ambient Air Temperature of 40°C (104°F) 

Temperature Rating of Conductor 
(See Table 310-61) 



Conductor 

Size 

(AWG or 

kcmil) 



2001-5000 Volts 
Ampacity 



90°C 
(194°F) 

Type 
MV-90 



105°C 
(221°F) 

Type 
MV-105 



65 

90 

120 

160 

185 



74 

99 

130 

175 

205 



5001-35,000 Volts 
Ampacity 



90°C 
(194°F) 

Type 
MV-90 



100 
130 
170 
195 



105°C 

(221°F) 

Type 

MV-105 



110 
140 
195 

225 



1/0 


215 


240 


225 


255 


2/0 


250 


275 


260 


295 


3/0 


290 


320 


300 


340 


4/0 


335 


375 


345 


390 



250 


375 


415 


380 


430 


350 


465 


515 


470 


525 


500 


580 


645 


580 


650 


750 


750 


835 


730 


820 


1000 


880 


980 


850 


950 



Table 310-69. Ampacities of Insulated Single Copper Conductor 
Isolated in Air Based on Conductor Temperatures of 90°C (194°F) 
and 105°C (221°F) and Ambient Air Temperature of 40°C (104°F) 

Temperature Rating of Conductor 
(See Table 310-61) 

2001-5000 Volts 5001-15,000 Volts 15,001-35,000 
Ampacity Ampacity Volts Ampacity 



Conductor 

Size 

(AWG or 

kcmil) 



90°C 105°C 

(194°F) (221°F) 

Type Type 

MV-90 MV-105 



90°C 
(194°F) 

Type 
MV-90 



105°C 
(221°F) 

Type 
MV-105 



90°C 105°C 

(194°F) (221°F) 

Type Type 

MV-90 MV-105 



83 
110 
145 
190 

225 



93 
120 
160 
215 
250 



110 
150 
195 

225 



125 
165 
215 
250 



225 



250 



1/0 


260 


290 


260 


290 


260 


290 


2/0 


300 


330 


300 


335 


300 


330 


3/0 


345 


385 


345 


385 


345 


380 


4/0 


400 


445 


400 


445 


395 


445 


250 


445 


495 


445 


495 


440 


490 


350 


550 


615 


550 


610 


545 


605 


500 


695 


775 


685 


765 


680 


755 


750 


900 


1000 


885 


990 


870 


970 



1000 


1075 


1200 


1060 


1185 


1040 


1160 


1250 


1230 


1370 


1210 


1350 


1185 


1320 


1500 


1365 


1525 


1345 


1500 


1315 


1465 


1750 


1495 


1665 


1470 


1640 


1430 


1595 


2000 


1605 


1790 


1575 


1755 


1535 


1710 



Table 310-68. Ampacities of Insulated Single Aluminum 
Conductor Cables Triplexed in Air Based on Conductor 
Temperatures of 90°C (194°F) and 105°C (221°F) and Ambient 
Air Temperature of 40°C (104°F) 







Temperature Rating of Conductor 






(See Table 310-61) 






2001 


-5000 Volts 


5001- 


35,000 Volts 




Ampacity 


Ampacity 


Conductor 


90°C 


105°C 


90°C 


105°C 


Size 


(194°F) 


(221°F) 


(194°F) 


(221°F) 


(AWG or 


Type 


Type 


Type 


Type 


kcmil) 


MV-90 


MV-105 


MV-90 


MV-105 


8 


50 


57 





_ 


6 


70 


77 


75 


84 


4 


90 


100 


100 


110 


2 


125 


135 


130 


150 


1 


145 


160 


150 


175 


1/0 


170 


185 


175 


200 


2/0 


195 


215 


200 


230 


3/0 


225 


250 


230 


265 


4/0 


265 


290 


270 


305 


250 


295 


325 


300 


335 


350 


365 


405 


370 


415 


500 


460 


510 


460 


515 


750 


600 


665 


590 


660 


1000 


715 


800 


700 


780 



Table 310-70. Ampacities of Insulated Single Aluminum 
Conductor Isolated in Air Based on Conductor Temperatures of 
90°C (194°F) and 105°C (221°F) and Ambient Air Temperature of 
40°C (104°F) 







Temperature Rating of Conductor 










(See Table 310-61) 








2001-5000 Volts 


5001-15,000 Volts 


15,001-35,000 




Ampacity 


Ampacity 


Volts A 
90°C 


mpacity 


Conductor 


90°C 


105°C 


90°C 


105°C 


105°C 


Size 


(194°F) 


(221°F) 


(194°F) 


(221°F) 


(194°F) 


(221°F) 


(AWG or 


Type 


Type 


Type 


Type 


Type 


Type 


kcmil) 


MV-90 


MV-105 


MV-90 


MV-105 


MV-90 


MV-105 


8 


64 


71 




_ 


_ 


_ • 


6 


85 


95 


87 


97 


— 


— 


4 


115 


125 


115 


130 


— 


— 


2 


150 


165 


150 


170 


— 


— 


1 


175 


195 


175 


195 


175 


195 



1/0 


200 


225 


200 


225 


200 


225 


2/0 


230 


260 


235 


260 


230 


260 


3/0 


270 


300 


270 


300 


270 


300 


4/0 


310 


350 


310 


350 


310 


345 


250 


345 


385 


345 


385 


345 


380 


350 


430 


480 


430 


480 


430 


475 


500 


545 


605 


535 


600 


530 


590 


750 


710 


790 


700 


780 


685 


765 



NATIONAL ELECTRICAL CODE 



1000 


855 


950 


840 


940 


825 


920 


1250 


980 


1095 


970 


1080 


950 


1055 


1500 


1105 


1230 


1085 


1215 


1060 


1180 


1750 


1215 


1355 


1195 


1335 


1165 


1300 


2000 


1320 


1475 


1295 


1445 


1265 


1410 












1999 Edition 



70-134 



ARTICLE 310 — CONDUCTORS FOR GENERAL WIRING 



Table 310-71. Ampacities of an Insulated Three-Conductor 
Copper Cable Isolated in Air Based on Conductor 
Temperatures of 90°C (194°F) and 105°C (221°F) and Ambient 
Air Temperature of 40°C (104°F) 



Table 310-73. Ampacities of an Insulated Triplexed or Three 
Single-Conductor Copper Cables in Isolated Conduit in Air 
Based on Conductor Temperatures of 90°C (194°F) and 105°C 
(221°F) and Ambient Air Temperature of 40°C (104°F) 







Temperature Rating of Conductor 






Temperature Rating 


; of Conductor 






(See Table 310-61) 








(See Table 310-61) 






2001 


-5000 Volts 


5001- 


35,000 Volts 


2001 


-5000 Volts 


5001- 


35,000 Volts 




Ampacity 


Ampacity 


Conductor 


Ampacity 


Ampacity 


Conductor 


90°C 


105°C 


90°C 


105°C 


90°C 


105°C 


90°C 


105°C 


Size 


(194°F) 


(221°F) 


(194°F) 


(221°F) 


Size 


(194°F) 


(221°F) 


(194°F) 


■ (221°F) 


(AWG or 


Type 


Type 


Type 


Type 


(AWG or 


Type 


Type 


Type 


Type 


kcmil) 


MV-90 


MV-105 


MV-90 


MV-105 


kcmil) 


MV-90 


MV-105 


MV-90 


MV-105 


8 


59 


66 


_ 




8 


55 


61 






6 


79 


88 


93 


105 


6 


75 


84 


83 


93 


4 


105 


115 


120 


135 


4 


97 


110 


110 


120 


2 


140 


154 


165 


185 


2 


130 


145 


150 


165 


1 


160 


180 


185 


210 


1 


155 


175 


170 


190 


1/0 


185 


205 


215 


240 


1/0 


180 


200 


195 


215 


2/0 


215 


240 


245 


275 


2/0 


205 


225 


225 


255 


3/0 


250 


280 


285 


315 


3/0 


240 


270 


260 


290 


4/0 


285 


320 


325 


360 


4/0 


280 


305 


295 


330 


250 


320 


355 


360 


400 


250 


315 


355 


330 


• 365 


350 


395 


440 


435 


490 


350 


385 


430 


395 


440 


500 


485 


545 


535 


600 


500 


475 


530 


480 


535 


750 


615 


685 


670 


745 


750 


600 


665 


585 


655 


1000 


705 


790 


770 


860 


1000 


690 


770 


675 


755 



• 



• 



Table 310-72. Ampacities of Insulated Three-Conductor 
Aluminum Cable Isolated in Air Based on Conductor 
Temperatures of 90°C (194°F) and 105°C (221°F) and Ambient 
Air Temperature of 40°C (104°F) 



Table 310-74. Ampacities of an Insulated Triplexed or Three 
Single-Conductor Aluminum Cables in Isolated Conduit in Air 
Based on Conductor Temperatures of 90°C (194°F) and 105°C 
(221°F) and Ambient Air Temperature of 40°C (104°F) 







Temperature Rating of Conductor 








Temperature Rating of Conductor 






(See Table 310-61) 








(See Table 310-61) 






2001 


-5000 Volts 


5001-35,000 Volts 


2001 


-5000 Volts 


5001- 


35,000 Volts 




Ampacity 


Ampacity 


Conductor 


Ampacity 


Ampacity 


Conductor 


90°C 


105°C 


90°C 


105°C 


90°C 


105°C 


90°C 


105°C 


Size 


(194°F) 


(221°F) 


(194°F) 


(221°F) 


Size 


(194°F) 


(221°F) 


(194°F) 


(221°F) 


(AWG or 


Type 


Type 


Type 


Type 


(AWG or 


Type 


Type 


Type 


Type 


kcmil) 


MV-90 


MV-105 


MV-90 


MV-105 


kcmil) 


MV-90 


MV-105 


MV-90 


MV-105 


8 


46 


51 








8 


43 


48 








6 


61 


68 


72 


80 


6 


58 


65 


65 


72 


4 


81 


90 


95 


105 


4 


76 


85 


84 


94 


2 


110 


120 


125 


145 


2 


100 


115 


115 


130 


1 


125 


140 


145 


165 


1 


120 


135 


130 


150 


1/0 


145 


160 


170 


185 


1/0 


140 


155 


150 


170 


2/0 


170 


185 


190 


215 


2/0 


160 


175 


175 


200 


3/0 


195 


215 


220 


245 


3/0 


190 


210 


200 


225 


4/0 


225 


250 


255 


285 


4/0 


215 


240 


230 


260 


250 


250 


280 


280 


315 


250 


250 


280 


255 


290 


350 


310 


345 


345 


385 


350 


305 


340 


310 


350 


500 


385 


430 


425 


475 


500 


380 


425 


385 


430 


750 


495 


550 


540 


600 


750 


490 


545 


485 


540 


1000 


585 


650 


635 


705 


1000 


580 


645 


565 


640 



1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 310 — CONDUCTORS FOR GENERAL WIRING 



70-135 



Table 310-75. Ampacities of an Insulated Three-Conductor 
Copper Cable in Isolated Conduit in Air Based on Conductor 
Temperatures of 90°C (194°F) and 105°C (221°F) and Ambient 
Air Temperature of 40°C (104°F) 

Temperature Rating of Conductor 
(See Table 310-61) 





2001- 


-5000 Volts 


5001- 


35,000 Volts 




Ampacity 


Ampacity 


Conductor 


90°C 


105°C 


90°C 


105°C 


Size 


(194°F) 


(221°F) 


(194°F) 


(221°F) 


(AWG or 


Type 


Type 


Type 


Type 


kcmil) 


MV-90 


MV-105 


MV-90 


MV-105 


8 


52 


58 


_ 




6 


69 


77 


83 


92 


4 


91 


100 


105 


120 


2 


125 


135 


145 


165 


1 


140 


155 


165 


185 


1/0 


165 


185 


195 


215 


2/0 


190 


210 


220 


.245 


3/0 


220 


245 


250 


280 


4/0 


255 


285 


290 


320 


250 


280 


315 


315 


350 


350 


350 


390 


385 


430 


500 


425 


475 


470 


525' ■ 


750 


525 


585 


570 


635 


1000 


590 


660 


650 


725 



Table 310-76. Ampacities of an Insulated Three- Conductor 
Aluminum Cable in Isolated Conduit in Air Based on 
Conductor Temperatures of 90°C (194°F) and 105°C (221°F) 
and Ambient Air Temperature of 40°C (104°F) 

Temperature Rating of Conductor 
(See Table 310-61) 





2001- 


-5000 Volts 


5001- 


35,000 Volts 




Ampacity 


Ampacity 


Conductor 


90°C 


105°C 


90°C 


105°C 


Size 


(194°F) 


(221°F) 


(194°F) 


(221°F) 


(AWG or 


Type 


Type 


Type 


Type 


kcmil) 


MV-90 


MV-105 


MV-90 


MV-105 


8 


41 


46 







6 


53 


59 


64 


71 


4 


71 


79 


84 


94 


2 


96 


105 


115 


125 


1 


110 


125 


130 


145 


1/0 


130 


145 


150 


170 


. 2/0 


150 


165 


170 


190 


3/0 


170 


190 


195 


220 


4/0 


200 


225 


225 


255 


250 


220 


245 


250 


280 


350 


275 . 


305 


305 


340 


500 


340 


380 


380 


425 


750 


430 


480 


470 


520 


1000 


505 


560 


550 


615 



Table 310-77. Ampacities of Three Single-Insulated Copper 
Conductors in Underground Electrical Ducts (Three 
Conductors per Electrical Duct) Based on Ambient Earth 
Temperature of 20°C (68°F), Electrical Duct Arrangement per 
Figure 310-60, 100 Percent Load Factor, Thermal Resistance 
(RHO) of 90, Conductor Temperatures of 90°C (194°F) and 
105°C (221°F) 



Temperature Rating of Conductor 
(See Table 310-61) 



2001-5000 Volts 
Ampacity 



5001-35,000 Volts 
Ampacity 



Conductor Size 
(AWG or kcmil) 



90°C 

(194°F) 

Type 

MV-90 



105°C 

(221°F) 

Type 

MV-105 



90°C 
(194°F) 

Type 
MV-90 



One Circuit (See 

Figure 310-60, 

Detail 1) 



250 
350 
500 
750 
1000 



Three Circuits (See 

Figure 310-60, 

Detail 2) 



Six Circuits (See 

Figure 310-60, 

Detail 3) 



250 
350 
500 
750 
1000 



64 

85 

110 

145 

170 



56 

73 

95 

125 

140 



48 

62 

80 

105 

115 



69 

92 

120 

155 

180 



60 

79 

100 

130 

150 



52 

67 

86 

110 

125 



90 
115 
155 
175 



77 

99 

130 

145 



64 

82 

105 

120 



105°C 

(221°F) 

Type 

MV-105 



97 
125 
165 
185 



1/0 


195 


210 


200 


215 


2/0 


220 


235 


230 


245 


3/0 


250 


270 


260 


275 


4/0 


290 


310 


295 


315 



320 


345 


325 


345 


385 


415 


390 


415 


470 


• 505 


465 


500 


585 


630 


565 


610 


670 


720 


640 


690 



83 
105 
135 
155 



1/0 


160 


175 


165 


175 


2/0 


185 


195 


185 


200 


3/0 


210 


225 


210 


225 


4/0 


235 


255 


240 


255 



250 


260 


280 


260 


280 


350 


315 


335 


310 


330 


500 


375 


405 


370 


395 


750 


460 


495 


440 


475 


1000 


525 


565 


495 


535 



68 

88 

115 

125 



1/0 


135 


145 


135 


145 


2/0 


150 


160 


150 


165 


3/0 


170 


185 


170 


185 


4/0 


195 


210 


190 


205 



210 


225 


210 


225 


250 


270 


245 


265 


300 


325 


290 


310 


365 


395 


350 


375 


410 


445 


390 


415 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-136 



ARTICLE 310 — CONDUCTORS FOR GENERAL WIRING 



Table 310-78. Ampacities of Three Single-Insulated Aluminum 
Conductors in Underground Electrical Ducts (Three 
Conductors per Electrical Duct) Based on Ambient Earth 
Temperature of 20°C (68°F), Electrical Duct Arrangement per 
Figure 310-60, 100 Percent Load Factor, Thermal Resistance 
(RHO) of 90, Conductor Temperatures of 90°C (194°F) and 
105°C (221°F) 



Temperature Rating of Conductor 
(See Table 310-61) 



Conductor Size 
(AWG or kcmil) 



One Circuit (See 

Figure 310-60, 

Detail 1) 



250 
350 
500 
750 
1000 



Three Circuits 

(See Figure 310- 

60, Detail 2) 



250 
350 
500 
750 
1000 



Six Circuits (See 

Figure 310-60, 

Detail 3) 



250 
350 
500 
750 
1000 



2001-5000 Volts 
Ampacity 



5001-35,000 Volts 
Ampacity 



90°C 
(194°F) 

Type 
MV-90 



105°C 

(221°F) 

Type 

MV-105 



90°C 
(194°F) 

Type 
MV-90 



250 
305 
370 
470 
545 



205 
245 
295 
370 
425 



165 
195 
240 
290 

335 



270 
325 
400 
505 
590 



220 
265 
320 
395 
460 



180 
210 
255 
315 
360 



250 
305 
370 
455 
525 



200 
245 
290 
355 
405 



165 
195 
230 
280 
320 



105°C 

(221°F) 

Type 

MV-105 



8 


50 


54 


— 


— 


6 


66 


71 


70 


75 


4 • 


86 


93 


91 


98 


2 


115 


125 


120 


130 


1 


130 


140 


135 


145 



1/0 


150 


160 


155 


165 


2/0 


170 


185 


175 


190 


3/0 


195 


210 


200 


215 


4/0 


225 


245 


230 


245 



270 
330 
400 
490 
565 



8 


44 


47 


— 


— 


6 


57 


61 


60 


65 


4 


74 


80 


77 


83 


2 


96 


105 


100 


105 


1 


110 


120 


110 


120 



1/0 


125 


135 


125 


140 


2/0 


145 


155 


145 


155 


3/0 


160 


175 


165 


175 


4/0 


185 


200 


185 


200 



220 
260 
315 
385 
440 



8 


38 


41 


— 


— 


6 


48 


52 


50 


54 


4 


. 62 


67 


64 


69 


2 


80 


86 


80 


88 


1 


91 


98 


90 


99 



1/0 


105 


110 


105 


110 


2/0 


115 


125 


115 


125 


3/0 


135 


.145 


130 


145 


4/0 


150 


165 


150 


160 



175 
210 
250 
305 

345 



Table 310-79. Ampacities of Three Insulated Copper 
Conductors Cabled within an Overall Covering (Three- 
Conductor Cable) in Underground Electrical Ducts (One 
Cable per Electrical Duct) Based on Ambient Earth 
Temperature of 20°C (68°F), Electrical Duct Arrangement 
per Figure 310-60, 100 Percent Load Factor, Thermal 
Resistance (RHO) of 90, Conductor Temperatures of 90°C 
(194°F) and 105°C (221°C) 



Temperature Rating of Conductor 
(See Table 310-61) 



2001-5000 Volts 
Ampacity 



5001-35,000 Volts 
Ampacity 



Conductor Size 
(AWG or kcmil) 



One Circuit (See 

Figure 310-60, 

Detail 1) 



250 
350 
500 
750 
1000 



Three Circuits 

(See Figure 310- 

60, Detail 2) 



250 
350 
500 
750 
1000 



Six Circuits (See 

Figure 310-60, 

Detail 3) 



250 
350 
500 
750 
1000 



90°C 
(194°F) 

Type 
MV-90 



105°C 

(221°F) 

Type 

MV-105 



90°C 
(194°F) 

Type 
MV-90 



290 
355 
430 
530 
600 



245 
295 
355 
430 
485 



200 
240 
290 
350 
390 



315 
380 
460 
570 
645 



265 
315 
380 
465 
520 



220 
270 
310 
375 
420 



310 
375 
450 
545 
615 



255 
305 
360 
430 
485 



205 
245 
290 
340 
380 



105°C 

(221°F) 

Type 

MV-105 



8 


59 


64 


— 


— 


6 


78 


84 


88 


95 


4 


100 


110 


115 


125 


2 


135 


145 


150 


160 


1 


155 


165 


170 


185 



1/0 


175 


190 


195 


210 


2/0 


200 


220 


220 


235 


3/0 


230 


250 


250 


270 


4/0 


265 


285 


285 


305 



335 
400 
485 
585 
660 



8 


53 


57 


— 


— 


6 


69 


74 


75 


81 


4 


89 


96 


97 


105 


2 


115 


125 


125 


135 


1 


135 


145 


140 


155 



1/0 


150 


165 


160 


175 


2/0 


170 


185 


185 


195 


3/0 


195 


210 


205 


220 


4/0 


225 


240 


230 


250 



270 
325 
385 
465 
515 



8 


46 


50 


— 


— 


6 


60 


65 


63 


68 


4 • 


77 


83 


81 


87 


2 


98 


105 


105 


110 


1 


110 


120 


115 


125 



1/0 


125 


135 


130 


145 


2/0 


145 


155 


150 


160 


3/0 


165 


175 


170 


180 


4/0 


185 


200 


190 


200 



220 
275 
305 
365 
405 



• 



• 



• 



• 



1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 310 — CONDUCTORS FOR GENERAL WIRING 



70-137 



Table 310-80. Ampacities of Three Insulated Aluminum 
Conductors Cabled within an Overall Covering (Three- 
Conductor Cable) in Underground Electrical Ducts (One Cable 
per Electrical Duct) Based on Ambient Earth Temperature of 
20°C (68°F), Electrical Duct Arrangement per Figure 310-60, 
100 Percent Load Factor, Thermal Resistance (RHO) of 90, 
Conductor Temperatures of 90°C (194°F) and 105°C (221°C) 



Temperature Rating of Conductor 
(See Table 310-61) 



Conductor Size 
(AWG or kcmil) 



One Circuit (See 

Figure 310-60, 

Detail 1) 



Three Circuits 

(See Figure 310- 

60, Detail 2) 



250 
350 
500 
750 
1000 



Six Circuits (See 

Figure 310-60, 

Detail 3) 



2001-5000 Volts 
Ampacity 



5001-35,000 Volts 
Ampacity 



90°C 
(194°F) 

Type 
MV-90 



105°C 
(221°F) 

Type 
MV-105 



46 

61 

80 

105 

120 



41 
54 
70 
90 
105 



190 
230 
280 
345 
400 



50 

66 

86 

110 

130 



44 
58 
75 
97 
110 



205 
250 
300 
375 
430 



90°C 
(194°F) 

Type 
MV-90 



69 

89 

115 

135 



59 

75 

100 

110 



200 
240 
285 
350 
400 



105°C 

(221°F) 

Type 

MV-105 



74 

96 

125 

145 



1/0 


140 


150 


150 


165 


2/0 


160 


170 


170 


185 


3/0 


180 


195 


195 


210 


4/0 


205 


220 


220 


240 



250 


230 


245 


245 


265 


350 


280 


310 


295 


315 


500 


340 


365 


355 


385 


750 


425 


460 


440 


475 


1000 


495 


535 


510 


545 



64 
• 81 
105 
120 



1/0 


120 


125 


125 


135 


2/0 


135 


145 


140 


155 


3/0 


155 


165 


160 


175 


4/0 


175 


185 


180 


195 



215 
255 
305 
375 
430 



8 


36 


39 


— 


— 


6 


46 


50 


49 


53 


4 


60 


65 


63 


68 


2 


77 


83 


80 


86 


1 


87 


94 


90 


98 



1/0 


99 


105 


105 


110 


2/0 


110 


120 


115 


125 


3/0 


130 


140 


130 


140 


4/0 


145 


155 


150 


160 



250 


160 


170 


160 


170 


350 


190 


205 


190 


205 


500 


230 


245 


230 


245 


750 


280 


305 


275 


295 


1000 


320 


345 


315 


335 



Table 310-81. Ampacities of Single Insulated Copper 
Conductors Directly Buried in Earth Based on Ambient Earth 
Temperature of 20°C (68°F), Arrangement per Figure 310-60, 
100 Percent Load Factor, Thermal Resistance (RHO) of 90, 
Conductor Temperatures of 90°C (194°F) and 105°C (221°C) 

Temperature Rating of Conductor 
(See Table 310-61) 



Conductor Size 
(AWG or kcmil) 



One Circuit, 

Three 

Conductors (See 

Figure 310-60, 

Detail 9) 



1/0 
2/0 
3/0 
4/0 



250 
350 
500 
750 
1000 



Two Circuits, 
Six Conductors 
(See Figure 310- 

60, Detail 10) 



1/0 
2/0 
3/0 
4/0 



250 
350 
500 
750 
1000 



2001-5000 Volts 
Ampacity 



5001-35,000 Volts 
Ampacity 



90°C 
(194°F) 

Type 
MV-90 



105°C 

(221°F) 

Type 

MV-105 



90°C 
(194°F) 

Type 
MV-90 



110 
140 
180 
230 
260 



295 
335 
385 
435 



470 
570 
690 
845 
980 



100 
130 
165 
215 
240 



275 
310 
355 
400 



435 
520 
630 
775 
890 



115 
150 
195> 
250 
280 



320 
365 
415 
465 



510 
615 
745 
910 
1055 



110 
140 
180 
230 
260 



295 
335 
380 
430 



470 
560 
680 
835 
960 



130 
170 
210 
240 



275 
310 
355 
405 



440 
535 
650 
805 
930 



120 
160 
195 

225 



255 
290 
330 
375 



410 
495 
600 
740 
855 



105°C 

(221°F) 

Type 

MV-105 



140 
180 
225 
260 



295 
335 
380 
435 



475 
575 
700 
865 
1005 



130 
170 
210 
240 



275 
315 
355 
405 



440 
530 
645 
795 
920 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-138 



ARTICLE 310 — CONDUCTORS FOR GENERAL WIRING 



Table 310-82. Ampacities of Single Insulated Aluminum 
Conductors Directly Buried in Earth Based on Ambient Earth 
Temperature of 20°C (68°F), Arrangement per Figure 310-60, 
100 Percent Load Factor, Thermal Resistance (RHO) of 90, 
Conductor Temperatures of 90°C (194°F) and 105°C (221°F) 

Temperature Rating of Conductor 
(See Table 310-61) 



Table 310-83. Ampacities of Three Insulated Copper 
Conductors Cabled within an Overall Covering (Three- 
Conductor Cable), Directly Buried in Earth Based on Ambient 
Earth Temperature of 20°C (68°F), Arrangement per Figure 
310-60, 100 Percent Load Factor, Thermal Resistance (RHO) 
of 90, Conductor Temperatures of 90°C (194°F) and 105°C 
(221°F) 















Temperature Rating of Conductor 




2001- 


5000 Volts 


5001-35,000 Volts 






(See Table 310-61) 






Ampacity 


Ampacity 
















2001-5000 Volts 


5001-: 














S5,000 Volts 




90°C 


105°C 


90°C 


105°C 




Ampacity 


Ampacity 




(194°F) 
Type 


(221°F) 
Type 


(194°F) 
Type 


(221°F) 
Type 












Conductor Size 




90°C 


105°C 


90°C 


105°C 


(AWG or kcmil) 


MV-90 


MV-105 


MV-90 


MV-105 




(194°F) 


(221°F) 


(194°F) 


(221°F) 












Conductor Size 


Type 


Type 


Type 


Type 


One Circuit, 










(AWG or kcmil) 


MV-90 


MV-105 


MV-90 


MV-105 


Three 




















Conductors (See 










One Circuit (See 










Figure 310-60, 










Figure 310-60, 










Detail 9) 










Detail 5) 










8 


85 


90 


— 


— 


8 


85 


89 




_ 


6 


110 


115 


100 


110 


6 


105 


115 


115 


120 


4 


140 


150 


130 


140 


4 


135 


150 


145 


155 


2 


180 


195 


165 


175 


2 


180 


190 


185 


200 


1 


205 


220 


185 


200 


1 


200 


215 


210 


225 


1/0 


230 


250 


215 


230 


1/0 


230 


245 


240 


255 


2/0 


265 


285 


245 


260 


2/0 


260 


280 


270 


290 


3/0 


300 


320 


275 


295 


3/0 


295 


320 


305 


330 


4/0 


' 340 


365 


315 


340 


4/0 


335 


360 


350 


375 


250 


370 


395 


345 


370 


250 


365 


395 


380 


410 


350 


445 


480 


415 


450 


350 


440 


475 


460 


495 


500 


540 


580 


510 


545 


500 


530 


570 


550 


590 


750 


665 


720 


635 


680 


750 


650 


700 


665 


720 


1000 


780 


840 


740 


795 


1000 


730 


785 


750 


810 


Two Circuits, 










Two Circuits 










Six Conductors 










(See Figure 310- 










(See Figure 310- 










60, Detail 10) 










60, Detail 10) 




















8 


80 


84 






















8 


80 


85 


— 


— 


6 


100 


105 


105 


115 


6 


100 


110 


95 


100 


4 


130 


140 


135 


145 


4 


130 


140 


125 


130 


2 


165 


180 


170 


185 


2 


•165 


180 


155 


165 


1 


185 


200 


195 


210 


1 


190 


200 


175 


190 






















1/0 


215 


230 


220 


235 


1/0 


215 


230 


200 


215 


2/0 


240 


260 


250 


270 


2/0 


245 


260 


225 


245 


3/0 


275 


295 


280 


305 


3/0 


275 


295 


255 


275 


4/0 


310 


335 


320 


345 


4/0 


310 


335 


290 


315 






















250 


340 


365 


350 


375 


250 


340 


365 


320 


345 


350 


410 


440 


420 


450 


350 


410 


440 


385 


415 


500 


490 


525 


500 


535 


500 


495 


530 


470 


505 


750 


595 


640 


605 


650 


750 


610 


655 


580 


625 


1000 


665 


715 


675 


730 


1000 


710 


765 


680 


730 

























• 



• 



1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 310 — CONDUCTORS FOR GENERAL WIRING 



70-139 



Table 310-84. Ampacities of Three Insulated Aluminum 
Conductors Cabled within an Overall Covering (Three- 
Conductor Cable), Directly Buried in Earth Based on Ambient 
Earth Temperature of 20°C (68°F), Arrangement per Figure 
310-60, 100 Percent Load Factor, Thermal Resistance (RHO) 
of 90, Conductor Temperatures of 90°C (194°F) and 105°C 
(221°F) 



• 



Table 310-85. Ampacities of Three Triplexed Single Insulated 
Copper Conductors Directly Buried in Earth Based on Ambient 
Earth Temperature of 20°C (68°F), Arrangement per Figure 
310-60, 100 Percent Load Factor, Thermal Resistance (RHO) 
of 90, Conductor Temperatures 90°C (194°F) and 105°C (221°F) 

Temperature Rating of Conductor 
(See Table 310-61) 





Temperature Rating of Conductor 
















(See Table 310-61) 






2001- 


5000 Volts 


5001-35,000 Volts 














Ampacity 


Ampacity 




2001- 


5000 Volts 


5001-35,000 Volts 














Ampacity 


Ampacity 




90°C 


105°C 


90°C 


105°C 














(194T) 


(221°F) 


(194°F) 


(221 P F) 














90°C 


105°C 


90°C 


105°C 


Conductor Size 


Type 


Type 


Type 


Type 




(194°F) 
Type 


(221°F) 
Type 


(194°F) 
Type 


(221°F) 
Type 


(AWG or kcmil) 


MV-90 


MV-105 


MV-90 


MV-105 


Conductor Size 












(AWG or kcmil) 


MV-90 


MV-105 


MV-90 


MV-105 


One Circuit, 
Three 






















One Circuit (See 










Conductors (See 










Figure 310-60, 










Figure 310-60, 










Detail 5) „ 










Detail 7) 










8 


65 


70 






8 


90 


95 


— 


— 


6 


80 


88 


90 


95 


6 


120 


130 


115 


120 


4 


105 


115 


115 


125 


4 


150 


165 


150 


160 


2 


140' 


150 


145 


155 


2 


195 


205 


190 


205 


1 


155 


170 


165 


175 


1 


225. 


240 


215 


230 


1/0 


180 


190 


185 


200 


1/0 


255 


270 


245 


260 


' 2/0 


205 


220 


210 


225 


2/0 


290. 


310 


275 


295 


3/0 


230 


250 


240 


260 


3/0 


330 


360 


315 


340 


4/0 


260 


280 


270 


295 


4/0 


375 


405 


360 


385 


250 


285 


310 


300 


320 


250 


410 


445 


390 


410 


350 


345 


375 


360 


390 


350 


490 


580 


470 


505 


500 


420 


450 


435 


470 


"500 


590 


635 


565 


605 


750 


520 


560 


540 


580 


750 


725 


780 


685 


740 


1000 


600 


650 


620 


665 


1000 


825 


885 


770 


830 


Two Circuits 










Two Circuits, 










(See Figure 310- 










Six Conductors 










60, Detail 6) 










(See Figure 310- 
60, Detail 8) 






















8 


60 


66 


. — 


— 






















6 


75 


83 


80 


95 


- ■ 8 


85 


90 


— 


— 


4 


100 


110 


105 


115 


. 6 ■ ' 


110 


115 


105 


115 


2 - ■ 


130 


140 


135 


145 


* 4 


140 


150 


140 


150 


1 


145 


155' 


150 


165 


2 


180 


195 


175 


190 












1 


205 


220 ' 


200 


215 


1/0 


165 


180 


170 


185 












2/0 


190 


205 


195 


210 


1/0 


235 


250 


225 


240 


3/0 


215 


230 


220 


240 


2/0 


265 


285 


■ 255 


275 


4/0 


245 


260 


250 


270 


3/0 


300 


320 


290 


315 












4/0 


340 


365 


325 


350 


250 


265 


285 


275 


295 












350 


320 


345 


330 


355 


250 


370 


395 


355 


380 


500 


385 


415 


395 


425 


350 


445 


480 


425 


455 


750 


480 


515 


485 


525 


500 


535 


575 


510 


545 


1000 


550 


590 , 


560 


600 


750 


650 


700 


615 


660 












1000 


740 


795 


690 


745 















NATIONAL ELECTRICAL CODE 



1999 Edition 



70-140 



ARTICLE 318 — CABLE TRAYS 



Table 310-86. Ampacities of Three Triplexed Single Insulated 
Copper Conductors Directly Buried in Earth Based on Ambient 
Earth Temperature of 20°C (68°F), Arrangement per Figure 
310-60, 100 Percent Load Factor, Thermal Resistance (RHO) 
of 90, Conductor Temperatures 90°C (194°F) and 105°C (221°F) 



Article 318 — Cable Trays 

318-1. Scope. This article covers cable tray systems, in- 
cluding ladder, ventilated trough, ventilated channel, solid 
bottom, and other similar structures. 





Temperature Rating of Conductor 






(See Table 310-61) 






2001- 


5000 Volts 


5001-35,000 Volts 




Ampacity 


Ampacity 




90°C 


105°C 


90°C 


105°C 




(194°F) 


(221°F) 


(194°F) 


(221°F) 


Conductor Size 


Type 


Type 


Type 


Type 


(AWG or kcmil) 


MV-90 


MV-105 


MV-90 


MV-105 


One Circuit, 










Three 










Conductors (See 










Figure 310-60, 










Detail 7) 








1 


8 


70 


75 


— 


_ 1 


6 


90 


100 


90 


95 


. 4 


120 


130 


115 


125 


2 


155 


165 


145 


155 


1 


175 


190 


165 


175 


1/0 


200 


210 


190 


205 


2/0 


225 


240 


215 


230 


3/0 


255 


275 


245 


265 


4/0 


290 


310 


280 


305 


250 


320 


350 


305 


325 


350 


385 


420 


370 


400 


500 


465 


500 


445 


480 


750 


580 


625 


550 


590 


1000 


670 


725 


635 


680 


Two Circuits, 










Six Conductors 










(See Figure 310- 










60, Detail 8) 








I 


8 


65 


70 


— 


_ 1 


6 


85 


95 


85 


90 


4 


110 


120 


105 


' 115 


2 


140 


150 


135 


145 


1 


160 . 


170 


155 


170 


1/0 


180 


195 


175 


190 


2/0 


205 


220 


200 


215 


3/0 


235 


250 


225 


245 


4/0 


265 


285 


255 


275 


250 


290 


310 


280 


300 


350 


350 


375 


335 


360 


500 


420 


455 


405 


435 


750 


520 


560 


485 


525 


1000 


600 


645 


565 


605 



318-2. Definition. 

Cable Tray System. A unit or assembly of units or sec- 
tions and associated fittings forming a rigid structural system 
used to securely fasten or support cables and raceways. 

318-3. Uses Permitted. Cable tray installations shall not 
be limited to industrial establishments. 

(a) Wiring Methods. The following shall be permitted to 
be installed in cable tray systems under the conditions de- 
scribed in their respective articles and sections: 



Section 



Optical fiber cables 
Other factory-assembled, 
multiconductor control, 
signal, or power cables that 
are specifically approved for 
installation in cable trays 
Rigid metal conduit 
Rigid nonmetallic conduit 



Article 



Armored cable 


333 


Electrical metallic tubing 


348 


Electrical nonmetallic tubing 


331 


Fire alarm cables 


760 


Flexible metal conduit 


350 


Flexible metallic tubing 


349 


Instrumentation tray cable 


727 


Intermediate metal conduit 


345 


Liquidtight flexible metal 


351 


conduit and liquidtight 




flexible nonmetallic conduit 




Metal-clad cable 


334 


Mineral-insulated, metal- 


330 


sheathed cable 




Multiconductor service- 


338 


entrance cable 




Multiconductor underground 


339 


feeder and branch-circuit 




cable 




Multipurpose and 


800 


communications cables 




Nonmetallic-sheathed cable 


336 


Power and control tray cable 


340 


Power- limited tray cable 725-6 1(c) and 


725-7 1(e) 



770 



346 

347 



(b) In Industrial Establishments. The wiring methods in 
Section 318-3(a) shall be permitted to be used in any indus- 
trial establishment under the conditions described in their 
respective articles. In industrial establishments only, where 
conditions of maintenance and supervision ensure that only 



• 



• 



1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 318 — CABLE TRAYS 



70-141 



qualified persons will service the installed cable tray system, 
any of the cables in (1) and (2) shall be permitted to be 
installed in ladder, ventilated trough, or ventilated channel 
cable trays. 

(1) Single Conductors. Single conductor cables shall 
be permitted to be installed in accordance with the following. 

(a) Single conductor cable shall be No. 1/0 or larger and 
shall be of a type listed and marked on the surface for 
use in cable trays. Where Nos. 1/0 through 4/0 single 
conductor cables are installed in ladder cable tray, the 
maximum allowable rung spacing for the ladder cable 
tray shall be 9 in. (229 mm). Where exposed to direct 
rays of the sun, cables shall be identified as being sun- 
light resistant. 

(b) Welding cables shall comply with the provisions of Arti- 
cle 630, Part D. 

(c) Single conductors used as equipment grounding conduc- 
tors shall be insulated, covered, or bare and they shall 
be No. 4 or larger. 

(2) Multiconductor. Multiconductor cables, Type MV 
(Article 326) where exposed to direct rays of the sun, shall 
be identified as being sunlight resistant. 

(c) Equipment Grounding Conductors. Metallic cable 
trays shall be permitted to be used as equipment grounding 
conductors where continuous maintenance and supervision 
ensure that qualified persons will service the installed cable 
tray system and the cable tray complies with provisions of 
Section 318-7. 

(d) Hazardous (Classified) Locations. Cable trays in haz- 
ardous (classified) locations shall contain only the cable 
types permitted in Sections 501-4, 502-4, 503-3, and 504- 
20. 

(e) Nonmetallic Cable Tray. Nonmetallic cable tray shall 
be permitted in corrosive areas and in areas requiring voltage 
isolation. 

318-4. Uses Not Permitted. Cable tray systems shall not 
be used in hoistways or where subject to severe physical 
damage. Cable tray systems shall not be used in environ- 
mental airspaces, except as permitted in Section 300-22, to 
support wiring methods recognized for use in such spaces. 

318-5. Construction Specifications. 

(a) Strength and Rigidity. Cable trays shall have suitable 
strength and rigidity to provide adequate support for all 
contained wiring. 



(b) Smooth Edges. Cable trays shall not have sharp edges, 
burrs, or projections that may damage the insulation or jack- 
ets of the wiring. 

(c) Corrosion Protection. Cable tray systems shall be cor- 
rosion resistant. If made of ferrous material, the system shall 
be protected from corrosion as required by Section 300-6. 

(d) Side Rails. Cable trays shall have side rails or equiva- 
lent structural members. 

(e) Fittings. Cable trays shall include fittings or other suit- 
able means for changes in direction and elevation of runs. 

(f) Nonmetallic Cable Tray. Nonmetallic cable trays shall 
be made of flame-retardant material. 

318-6. Installation. 

(a) Complete System. Cable trays shall be installed as a 
complete system. Field bends or modifications shall be made 
so that the electrical continuity of the cable tray system and 
support for the cables shall be maintained. Cable tray systems 
shall be permitted to have mechanically discontinuous seg- 
ments between cable tray runs or between cable tray runs 
and equipment. The system shall provide for the support of 
the cables in accordance with their corresponding articles. 

Where cable trays support individual conductors and 
where the conductors pass from one cable tray to another, 
or from a cable tray to raceways or to equipment where 
the conductors are terminated, the support distance between 
cable trays or between the cable tray and the equipment 
shall not exceed 6 ft (1.83 m). The conductors shall be 
secured to the cable tray(s) at the transition and they shall 
be protected, by guarding or by location, from physical 
damage. 

A bonding jumper sized in accordance with Section 250- 
102 shall connect the two sections of cable tray, or the cable 
tray and the raceway or equipment. Bonding shall be in 
accordance with Section 250-96. 

(b) Completed Before Installation. Each run of cable tray 
shall be completed before the installation of cables. 

(c) Supports. Supports shall be provided to prevent stress 
on cables where they enter raceways or other enclosures 
from cable tray systems. 

(d) Covers. In portions of runs where additional protection 
is required, covers or enclosures providing the required pro- 
tection shall be of a material that is compatible with the 
cable tray. 

(e) Multiconductor Cables Rated 600 Volts or Less. 

Multiconductor cables rated 600 volts or less shall be permit- 
ted to be installed in the same cable tray. 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-142 



ARTICLE 318 — CABLE TRAYS 



(f) Cables Rated Over 600 Volts. Cables rated over 600 
volts and those rated 600 volts or less installed in the same 
cable tray shall comply with either (1) or (2). 

(1) The cables rated over 600 volts are Type MC. 

(2) The cables rated over 600 volts are separated from 
the cables rated 600 volts or less by a solid fixed barrier of 
a material compatible with the cable tray. 

(g) Through Partitions and Walls. Cable trays shall be 
permitted to extend transversely through partitions and walls 
or vertically through platforms and floors in wet -or dry 
locations where the installations, complete with installed 
cables, are made in accordance with the requirements of 
Section 300-21. 

(h) Exposed and Accessible. Cable trays shall be exposed 
and accessible except as permitted by Section 318-6(g). 

(i) Adequate Access. Sufficient space shall be provided 
and maintained about cable trays to permit adequate access 
for installing and maintaining the cables. 

(j) Raceways, Cables, and Outlet Boxes Supported from 
Cable Trays. In industrial facilities where conditions of 
maintenance and supervision ensure only qualified persons 
will service the installation and where cable trays are de- 
signed to support the load, raceways, cables, and outlet boxes 
shall be permitted to be supported from cable trays. For 
raceway terminating at the tray, a listed cable tray clamp or 
adapter shall be used and no nearby support, such as a 
support within 3 ft (914 mm), shall be required. 

For raceway or cable running parallel to, but under or 
beside, a tray, support shall be in accordance with the require- 
ments of the appropriate raceway or cable article. 

For outlet boxes located under or beside a tray, support 
shall be in accordance with the requirements of Article 370. 



(2) The minimum cross-sectional area of cable trays shall 
conform to the requirements in Table 318-7(b)(2). 

Table 318-7(b)(2). Metal Area Requirements for Cable Trays 
Used as Equipment Grounding Conductors 



Maximum Fuse 






Ampere Rating, 
Circuit Breaker 






Ampere Trip Setting, 
or Circuit Breaker 






Protective Relay 

Ampere Trip Setting 

for Ground-Fault 

Protection of Any 

Cable Circuit in the 


Minimum Cross-Sectional 
Area of Metal 3 (in. 2 ) 


Steel Cable 


Aluminum 


Cable Tray System 


Trays 


Cable Trays 


. 60 


0.20 


0.20 


100 


0.40 


0.20 


200 


0.70 


0.20 


400 


1.00 


0.40 


600 


1.50 b 


0.40 


1000 


— 


0.60 


1200 


— 


1.00 


1600 


— 


1.50 


2000 


— 


2.00 b 



Note: For SI units, 1 in. 2 = 645 sq mm 2 . 

a Total cross-sectional area of both side rails for ladder or trough cable 

trays; or the minimum cross-sectional area of metal in channel cable 

trays or cable trays of one-piece construction. 

b Steel cable trays shall not be used as equipment grounding conductors 

for circuits with ground-fault protection above 600 amperes. Aluminum 

cable trays shall not be used as equipment grounding conductors for 

circuits with ground-fault protection above 2000 amperes. 

(3) All cable tray sections and fittings shall be legibly 
and durably marked to show the cross-sectional area of 
metal in channel cable trays, or cable trays of one-piece 
construction, and the total cross-sectional area of both side 
rails for ladder or trough cable trays. 

(4) Cable tray sections, fittings, and connected raceways 
shall be bonded in accordance with Section 250-96 using 
bolted mechanical connectors or bonding jumpers sized and 
installed in accordance with Section 250-102. 



• 



318-7. Grounding. 

(a) Metallic Cable Trays. Metallic cable trays that support 
electrical conductors shall be grounded as required for con- 
ductor enclosures in Article 250. 

(b). Steel or Aluminum Cable Tray Systems. Steel or alu- 
minum cable tray systems shall be permitted to be used 
as equipment grounding conductors provided that all the 
following requirements are met. 



(1) The cable tray sections and fittings shall be identified 
for grounding purposes. 



318-8. Cable Installation. 

(a) Cable Splices. Cable splices made and insulated by 
approved methods shall be permitted to be located within a 
cable tray provided they are accessible and do not project 
above the side rails. 

(b) Fastened Securely. In other than horizontal runs, the 
cables shall be fastened securely to transverse members of 
the cable trays. 

(c) Bushed Conduit and lubing. A box shall not be re- 
quired where cables or conductors are installed in bushed 
conduit and tubing used for support or for protection against 
physical damage. 



• 



1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 318 — CABLE TRAYS 



70-143 



(d) Connected in Parallel. Where single conductor cables 
comprising each phase or neutral of a circuit are connected 
in parallel as permitted in Section 310-4, the conductors 
shall be installed in groups consisting of not more than one 
conductor per phase or neutral to prevent current unbalance 
in the paralleled conductors due to inductive reactance. 

Single conductors shall be securely bound in circuit 
groups to prevent excessive movement due to fault-current 
magnetic forces unless single conductors are cabled together, 
such as triplexed assemblies. 

(e) Single Conductors. Where any of the single conductors 
installed in ladder or ventilated trough cable trays are Nos. 
1/0 through 4/0, all single conductors shall be installed in 
a single layer. Conductors that are bound together to com- 
prise each circuit group shall be permitted to be installed in 
other than a single layer. 

318-9. Number of Multiconductor Cables, Rated 2000 
Volts or Less, in Cable Trays. The number of multicon- 
ductor cables, rated 2000 volts or less, permitted in a single 
cable tray shall not exceed the requirements of this section. 
The conductor sizes herein apply to both aluminum and 
copper conductors. 

(a) Any Mixture of Cables. Where ladder or ventilated 
trough cable trays contain multiconductor power or lighting 
cables, or any mixture of multiconductor power, lighting, 
control, and signal cables, the maximum number of cables 
shall conform to the following. 

(1) Where all of the cables are No. 4/0 or larger, the sum 
of the diameters of all cables shall not exceed the cable tray 
width, and the cables shall be installed in a single layer. 

(2) Where all of the cables are smaller than No. 4/0, the 
sum of the cross-sectional areas of all cables shall not exceed 
the maximum allowable cable fill area in Column 1 of Table 
318-9 for the appropriate cable tray width. 

(3) Where No. 4/0 or larger cables are installed in the 
same cable tray with cables smaller than No. 4/0, the sum 
of the cross-sectional areas of all cables smaller than No. 
4/0 shall not exceed the maximum allowable fill area re- 
sulting from the computation in Column 2 of Table 318-9 
for the appropriate cable tray width. The No. 4/0 and larger 
cables shall be installed in a single layer, and no other cables 
shall be placed on them. 

(b) Multiconductor Control and/or Signal Cables Only. 

Where a ladder or ventilated trough cable tray, having a 
usable inside depth of 6 in. (152 mm) or less, contains 
multiconductor control and/or signal cables only, the sum 
of the cross-sectional areas of all cables at any cross section 
shall not exceed 50 percent of the interior cross-sectional 
area of the cable tray. A depth of 6 in. (152 mm) shall be 



Table 318-9. Allowable Cable Fill Area for Multiconductor 
Cables in Ladder, Ventilated Trough, or Solid Bottom Cable 
Trays for Cables Rated 2000 Volts or Less 





Maximum Allowable Fill Area for 






Multiconductor Cables 






Ladder or 


Ventilated 








~ Trough Cable Trays, 


Solid Bottom Cable Trays, 




Section 318-9(a) 


Section 318-9(c) 






Column 2 a 


Column 3 


Column 4 a 




Column 1 


Applicable 


Applicable 


Applicable 


Inside 


Applicable 


for Section 


for Section 


for Section 


Width of 


for Section 


318-9(a)(3) 


318-9(c)(2) 


318-9(c)(3) 


Cable 


318-9(a)(2) 


Only 


Only 


Only 


Tray (in.) 


Only (in. 2 ) 


(in. 2 ) 


(in. 2 ) 


(in. 2 ) 


6.0 


7.0 


7-(1.2 Sd) b 


5.5 


5.5-Sd b 


9.0 


10.5 


10.5-(L2 Sd) 


8.0 


8.0-Sd 


12.0 


14.0 


14-(1.2 Sd) 


11.0 


11.0-Sd 


18.0 


21.0 


2 HI. 2 Sd) 


16.5 


16.5-Sd 


24.0 


28.0 


28-(1.2 Sd) 


22.0 


22.0-Sd 


30.0 


35.0 


35-(1.2 Sd) 


27.5 


27.5-Sd 


36.0 


42.0 


42-(1.2 Sd) 


33.0 


33.0-Sd 



Note: For SI units, 1 in. 2 = 645 mm 2 . 

a The maximum allowable fill areas in Columns 2 and 4 shall be computed. 

For example, the maximum allowable fill, in square inches, for a 6-in. 

(152-mm) wide cable tray in Column 2 shall be 7 minus (1.2 multiplied 

by Sd). 

b The term Sd in Columns 2 and 4 is equal to the sum of the diameters, 

in inches, of all Nos. 4/0 and larger multiconductor cables in the same 

cable tray with smaller cables. 



used to compute the allowable interior cross-sectional area 
of any cable tray that has a usable inside depth of more than 
6 in. (152 mm). 

(c) Solid Bottom Cable Trays Containing Any Mixture. 

Where solid bottom cable trays contain multiconductor 
power or lighting cables, or any mixture of multiconductor 
power, lighting, control, and signal cables, the maximum 
number of cables shall conform to the following. 

(1) Where all of the cables are No. 4/0 or larger, the sum 
of the diameters of all cables shall not exceed 90 percent 
of the cable tray width, and the cables shall be installed in 
a single layer. 

(2) Where all of the cables are smaller than No. 4/0, the 
sum of the cross-sectional areas of all cables shall not exceed 
the maximum allowable cable fill area in Column 3 of Table 
318-9 for the appropriate cable tray width. 

(3) Where No. 4/0 or larger cables are installed in the 
same cable tray with cables smaller than No. 4/0, the sum 
of the cross-sectional areas of all cables smaller than No. 
4/0 shall not exceed the maximum allowable fill area re- 
sulting from the computation in Column 4 of Table 318-9 
for the appropriate cable tray width. The No. 4/0 and larger 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-144 



ARTICLE 3 1 8 — CABLE TRAYS 



cables shall be installed in a single layer, and no other cables 
shall be placed on them. 

(d) Solid Bottom Cable Tray — Multiconductor Control 
and/or Signal Cables Only. Where a solid bottom cable 
tray, having a usable inside depth of 6 in. (152 mm) or less, 
contains multiconductor control and/or signal cables only, 
the sum of the cross-sectional areas of all cables at any cross 
section shall not exceed 40 percent of the interior cross- 
sectional area of the cable tray. A depth of 6 in. (152 mm) 
shall be Used to compute the allowable interior cross- 
sectional area of any cable tray that has a usable inside depth 
of more than 6 in. (152 mm). 

(e) Ventilated Channel Cable Trays. Where ventilated 
channel cable trays contain multiconductor cables of any 
type, the following shall apply. 

(1) Where only one multiconductor cable is installed, the 
cross-sectional area shall not exceed the value specified in 
Column 1 of Table 318-9(e). 

(2) Where more than one multiconductor cable is in- 
stalled, the sum of the cross-sectional area of all cables 
shall not exceed the value specified in Column 2 of Table 
318-9(e). 

Table 318-9(e). Allowable Cable Fill Area for Multiconductor 
Cables in Ventilated Channel Cable Trays for Cables Rated 
2000 Volts or Less 

Maximum Allowable Fill Area 

for Multiconductor Cables 

(in. 2 ) 



Inside Width of 

Cable Tray 

(in.) 



Column 1 
One Cable 



Column 2 
More than 
One Cable 



3 


2.3 


1.3 


4 


4.5 


2.5 


6 


7.0 


3.8 



Note: For SI units, 1 in. 2 = 645 mm 2 . 



318-10. Number of Single Conductor Cables, Rated 2000 
Volts or Less, in Cable Trays. The number of single con- 
ductor cables, rated 2000 volts or less, permitted in a single 
cable tray section shall not exceed the requirements of this 
section. The single conductors, or conductor assemblies, 
shall be evenly distributed across the cable tray. The con- 
ductor sizes herein apply to both aluminum and copper 
conductors. 

(a) Ladder or Ventilated Trough Cable Trays. Where 
ladder or ventilated trough cable trays contain single con- 



ductor cables, the maximum number of single conductors 
shall conform to the following. 

(1) Where all of the cables are 1000 kcmil or larger, the 
sum of the. diameters of all single conductor cables shall not 
exceed the cable tray width. 

(2) Where all of the cables are from 250 kcmil up to 
1000 kcmil, the sum of the cross-sectional areas of all single 
conductor cables shall not exceed the maximum allowable 
cable fill area in Column 1 of Table 318-10, for the appro- 
priate cable tray width. 

(3) Where 1000 kcmil or larger single conductor cables 
are installed in the same cable tray with single conductor 
cables smaller than 1000 kcmil, the sum of the cross-sec- 
tional areas of all cables smaller than 1000 kcmil shall not 
exceed the maximum allowable fill area resulting from the 
computation in Column 2 of Table 318-10, for the appropri- 
ate cable tray width. 

(4) Where any of the single conductor cables are Nos. 
1/0 through 4/0, the sum of the diameters of all single 
conductor cables shall not exceed the cable tray width. 

(b) Ventilated Channel Cable Trays. Where 3-in. 
(76-mm), 4-in. (102-mm), or 6-in. (152-mm) wide ventilated 
channel cable trays contain single conductor cables, the sum 
of the diameters of all single conductors shall not exceed 
the inside width of the channel. 



Table 318-10. Allowable Cable Fill Area for Single Conductor 
Cables in Ladder or Ventilated Trough Cable Trays for Cables 
Rated 2000 Volts or Less 



Maximum Allowable Fill Area for Single 

Conductor Cables in Ladder or Ventilated Trough 

Cable Trays 





Column 1 


Column 2 a 


Inside 


Applicable for 


Applicable for 


Width of 


Section 318-10(a)(2) 


Section 318-10(a)(3) 


Cable Tray 


Only 


Only 


(in.) 


(iii. 2 ) 


(in. 2 ) 


6 


6.5 


6.5-(l.l Sd) b 


9 


9.5 


9.5-(l.l Sd) 


12 


13.0 


1 3.0-0 :1 Sd) 


18 


19.5 


19.5-(1.1 Sd) 


24 


26.0 


26.0-0.1 Sd) 


30 


32.5 


32.5-0-1 Sd) 


36 


39.0 


39.0-01 Sd) 



Note: For SI units, 1 in. 2 = 645 mm 2 . 

a The maximum allowable fill areas in Column 2 shall be computed. For 
example, the maximum allowable fill, in square inches, for a 6-in. (152- 
mm) wide cable tray shall be 6.5 minus (1.1 multiplied by Sd). 
b The term Sd in Column 2 is equal to the sum of the diameters, in inches, 
of all 1000 kcmil and larger single conductor cables in the same ladder or 
ventilated trough cable tray with small cables. 



1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 318 — CABLE TRAYS 



70-145 



318-11. Ampacity of Cables, Rated 2000 Volts or Less, 
in Cable Trays. 

(a) Multiconductor Cables. The allowable ampacity of 
multiconductor cables, nominally rated 2000 volts or less, 
installed according to the requirements of Section 318-9, 
shall be as given in Tables 310-16 and 310-18, subject to 
the provisions of (1), (2), and (3). 

(1) The derating factors of Section 3 10- 15(b)(2)(a) shall 
apply only to multiconductor cables with more than three 
current-carrying conductors. Derating shall be limited to the 
number of current-carrying conductors in the cable and not 
to the number of conductors in the cable tray. 

(2) Where cable trays are continuously covered for more 
than 6 ft (1.83 m) with solid un ventilated covers, not over 
95 percent of the allowable ampacities of Tables 310-16 and 
310-18 shall be permitted for multiconductor cables. 

(3) Where multiconductor cables are installed in a single 
layer in uncovered trays, with a maintained spacing of not 
less than one cable diameter between cables, the ampacity 
shall not exceed the allowable ambient temperature-cor- 
rected ampacities of multiconductor cables, with not more 
than three insulated conductors rated through 2000 volts 
in free air, in accordance with Section 3 10- 15(c). 

FPN: See Table B-3 10-3 in Appendix B. 

(b) Single Conductor Cables. The derating factors of Sec- 
tion 3 10- 15(b)(2)(a), shall not apply to the ampacity of cables 
in cable trays. The ampacity of single conductor cables, or 
single conductors cabled together (triplexed, quadruplexed, 
etc.), nominally rated 2000 volts or less, shall comply with 
the following. 

(1) Where installed according to the requirements of Sec- 
tion 318-10, the ampacities for 600 kcmil and larger single 
conductor cables in uncovered cable trays shall not exceed 
75 percent of the allowable ampacities in Tables 310-17 and 
310-19. Where cable trays are continuously covered for 
more than 6 ft (1.83 m) with solid un ventilated covers, the 
ampacities for 600 kcmil and larger cables shall not exceed 
70 percent of the allowable ampacities in Tables 310-17 and 
310-19. 

(2) Where installed according to the requirements of Sec- 
tion 318-10, the ampacities for No. 1/0 through 500 kcmil 
single conductor cables in uncovered cable trays shall not 
exceed 65 percent of the allowable ampacities in Tables 310- 
17 and 310-19. Where cable trays are continuously covered 
for more than 6 ft (1.83 m) with solid unventilated covers, 
the ampacities for No. 1/0 through 500 kcmil cables shall 
not exceed 60 percent of the allowable ampacities in Tables 
310-17 and 310-19. 



(3) Where single conductors are installed in a single layer 
in uncovered cable trays, with a maintained space of not 
less than one cable diameter between individual conductors, 
the ampacity of Nos. 1/0 and larger cables shall not exceed 
the allowable ampacities in Tables 310-17 and 310-19. 

(4) Where single conductors are installed in a triangular 
or square configuration in uncovered cable trays, with a 
maintained free air space of not less than 2.15 times one 
conductor diameter (2.15 X O.D.) of the largest conductor 
contained within the configuration and adjacent conductor 
configurations or cables, the ampacity of Nos. 1/0 and larger 
cables shall not exceed the allowable ampacities of two or 
three single insulated conductors rated through 2000 volts 
supported on a messenger in accordance with Section 310- 
15(b). 

FPN: See Table 310-20. 

318-12. Number of Type MV and Type MC Cables (2001 
Volts or Over) in Cable Trays. The number of cables, 
rated 2001 volts or over, permitted in a single cable tray 
shall not exceed the requirements of this section. 

The sum of the diameters of single conductor and multi- 
conductor cables shall not exceed the cable tray width, and 
the cables shall be installed in a single layer. Where single 
conductor cables are triplexed, quadruplexed, or bound to- 
gether in circuit groups, the sum of the diameters of the 
single conductors shall not exceed the cable tray width, and 
these groups shall be installed in single layer arrangement. 

318-13. Ampacity of Type MV and Type MC Cables 
(2001 Volts or Over) in Cable Trays. The ampacity of 
cables, rated 2001 volts, nominal, or over, installed according 
to Section 318-12 shall not exceed the requirements of this 
section. 

(a) Multiconductor Cables (2001 Volts or Over). The al- 
lowable ampacity of multiconductor cables shall be as given 
in Tables 310-75 and 310-76, subject to the provisions of 
(1) and (2). 

(1) Where cable trays are continuously covered for more 
than 6 ft (1.83 m) with solid unventilated covers, not more 
than 95 percent of the allowable ampacities of Tables 310- 
75 and 310-76 shall be permitted for multiconductor cables. 

(2) Where multiconductor cables are installed in a single 
layer in uncovered cable trays, with maintained spacing of 
not less than one cable diameter between cables, the ampac- 
ity shall not exceed the allowable ampacities of Tables 310- 
71 and 3 10-72. 

(b) Single Conductor Cables (2001 Volts or Over). The 

ampacity of single conductor cables, or single conductors 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-146 



ARTICLE 320 — OPEN WIRING ON INSULATORS 



cabled together (triplexed, quadruplexed, etc.), shall comply 
with the following. 

(1) The ampacities for Nos. 1/0 and larger single conduc- 
tor cables in uncovered cable trays shall not exceed 75 
percent of the allowable ampacities in Tables 310-69 and 
310-70. Where the cable trays are covered for more than 6 
ft (1.83 m) with solid unventilated covers, the ampacities 
for Nos. 1/0 and larger single conductor cables shall not 
exceed 70 percent of the allowable ampacities in Tables 310- 
69 and 310-70. 

(2) Where single conductor cables are installed in a single 
layer in uncovered cable trays, with a maintained space of 
not less than one cable diameter between individual con- 
ductors, the ampacity of Nos. 1/0 and larger cables shall not 
exceed the allowable ampacities in Tables 310-69 and 310- 
70. 

(3) Where single conductors are installed in a triangular 
or square configuration in uncovered cable trays, with a 
maintained free air space of not less than 2.15 times the 
diameter (2.15 X O.D.) of the largest conductor contained 
within the configuration and adjacent conductor configura- 
tions or cables, the ampacity of Nos, 1/0 and larger cables 
shall not exceed the allowable ampacities in Tables 310-67 
and 310-68. 



Article 320 — Open Wiring on Insulators 

320-1. Definition. Open wiring on insulators is an exposed 
wiring method using cleats, knobs, tubes, and flexible tubing 
for the protection and support of single insulated conductors 
run in or on buildings, and not concealed by the building 
structure. 

320-2. Other Articles. Open wiring on insulators shall 
comply with this article and also with the applicable provi- 
sions of other articles in this Code, especially Articles 225 
and 300. 

320-3. Uses Permitted. Open wiring on insulators shall be 
permitted on systems of 600 volts, nominal, or less, only 
for industrial or agricultural establishments, indoors or out- 
doors, in wet or dry locations, where subject to corrosive 
vapors, and for services. 

320-5. Conductors. 

(a) Type. Conductors shall be of a type specified by Article 
310. 

(b) Ampacity. The ampacity shall comply with Section 
310-15. 



320-6. Conductor Supports. 

(a) Conductor Sizes Smaller than No. 8. Conductors 
smaller than No. 8 shall be rigidly supported on noncombus- 
tible, nonabsorbent insulating materials and shall not contact 
any other objects. 
• Supports shall be installed as follows: 

(1) Within 6 in. (152 mm) from a tap or splice 

(2) Within 12 in. (305 mm) of a dead-end connection to a 
lampholder or receptacle 

(3) At intervals not exceeding 4!/2 ft (1.37 m) and at closer 
intervals sufficient to provide adequate support where 
likely to be disturbed 



(b) Conductor Sizes No. 8 and Larger. Supports for con- 
ductors No. 8 or larger installed across open spaces shall be 
permitted up to 15 ft (4.57 m) apart if noncombustible, 
nonabsorbent insulating spacers are used at least every 
4'/2 ft (1.37 m) to maintain at least 2 l A in. (64 mm) between 
conductors. 

Where not likely to be disturbed in buildings of mill 
construction, No. 8 and larger conductors shall be permitted 
to be run across open spaces if supported from each wood 
cross member on approved insulators maintaining 6 in. 
(152 nun) between conductors. 

(c) Industrial Establishments. In industrial establish- 
ments only, where conditions of maintenance and supervi- 
sion ensure that only qualified persons will service the 
system, conductors of sizes 250 kcmil and larger shall be 
permitted to be run across open spaces where supported on 
intervals up to 30 ft (9.1 m) apart. 

320-7. Mounting of Conductor Supports. Where nails 
are used to mount knobs, they shall not be smaller than 
tenpenny. Where screws are used to mount knobs, or where 
nails or screws are used to mount cleats, they shall be of a 
length sufficient to penetrate the wood to a depth equal to 
at least one-half the height of the knob and the full thickness 
of the cleat. Cushion washers shall be used with nails. - 

320-8. Tie Wires. No. 8 or larger conductors supported on 
solid knobs shall be securely tied thereto by tie wires having 
an insulation equivalent to that of the conductor. 

320-10. Flexible Nonmetallic Tubing. In dry locations, 
where not exposed to severe physical damage, conductors 
shall be permitted to be separately enclosed in flexible non- 
metallic tubing. The tubing shall be in continuous lengths 
not exceeding 15 ft (4.57 m) and secured to the surface by 
straps at intervals not exceeding 4Yi ft (1.37 m). 



• 



• 



• 



1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 321 —MESSENGER SUPPORTED WIRING 



70-147 



• 



320-11. Through Walls, Floors, Wood Cross Members, 
etc. Open conductors shall be separated from contact with 
walls, floors, wood cross members, or partitions through 
which they pass by tubes or bushings of noncombustible, 
nonabsorbent insulating material. Where the bushing is 
shorter than the hole, a waterproof sleeve of noninductive 
material shall be inserted in the hole and an insulating bush- 
ing slipped into the sleeye at each end in such a manner as 
to keep the conductors absolutely out of contact with the 
sleeve. Each conductor shall be carried through a separate 
tube or sleeve. 

FPN: See Section 310-10 for temperature limitation of 
conductors. 

320-12. Clearance from Piping, Exposed Conductors, 
etc. Open conductors shall be separated at least 2 in. (50.8 
mm) from metal raceways, piping, or other conducting mate- 
rial, and from any exposed lighting, power, or signaling 
conductor, or shall be separated therefrom by a continuous 
and firmly fixed nonconductor in addition to the insulation 
of the conductor. Where any insulating tube is used, it shall 
be secured at the ends. Where practicable, conductors shall 
pass over rather than under any piping subject to leakage 
or accumulations of moisture. 

320-13. Entering Spaces Subject to Dampness, Wetness, 
or Corrosive Vapors. Conductors entering or leaving loca- . 
tions subject to dampness, wetness, or corrosive vapors shall 
have drip loops formed on them and shall then pass upward 
and inward from the outside of the buildings, or from the 
damp, wet, or corrosive location, through noncombustible, 
nonabsorbent insulating tubes. 

FPN: See Section 230-52 for individual conductors entering 
buildings or other structures. 

320-14. Protection from Physical Damage. Conductors 
within 7 ft (2.13 m) from the floor shall be considered 
exposed to physical damage. Where open conductors cross 
ceiling joists and wall studs and are exposed to physical 
damage, they shall be protected by one of the following 
methods: 



(3) Boxing made as above and furnished with a cover kept 
at least 1 in. (25.4 mm) away from the conductors within. 
Where protecting vertical conductors on side walls, the 
boxing shall be closed at the top and the holes through 
which the conductors pass shall be bushed. 

(4) Rigid metal conduit, intermediate metal conduit, rigid 
nonmetallic conduit, or electrical metallic tubing, in 
which case the rules of Articles 345, 346, 347, or 348 
shall apply; or by metal piping, in which case the con- 
ductors shall be encased in continuous lengths of ap- 
proved flexible tubing. 

320-15. Unfinished Attics and Roof Spaces. Conductors 
in unfinished attics and roof spaces shall comply with (a) 
or (b).. 

(a) Accessible by Stairway or Permanent Ladder. Con- 
ductors shall be installed along the side of or through bored 
holes in floor joists, studs, or rafters. Where run through 
bored holes, conductors in the joists and in studs or rafters 
to a height of not less than 7 ft (2.13 m) above the floor or 
floor joists shall be protected by substantial running boards 
extending not less than 1 in. (25.4 mm) on each side of the 
conductors. Running boards shall be securely fastened in 
place. Running boards and guard strips shall not be required 
for conductors installed along the sides of joists, studs, or 
rafters. 

(b) Not Accessible by Stairway or Permanent Ladder. 

Conductors shall be installed along the sides of or through 
bored holes in floor joists, studs, or rafters. 

Exception: In buildings completed before the wiring is in- 
stalled, attic and roof spaces that are not accessible by 
stairway or permanent ladder and have headroom at all 
points less than 3 ft (914 mm), the wiring shall be permitted 
to be installed on the edges of rafters or joists facing the 
attic or roof space. 

320-16. Switches. Surface-type snap switches shall be 
mounted in accordance with Section 380- 10(a), and boxes 
shall not be required. Other type switches shall be installed 
in accordance with Section 380-4. 



(1) Guard strips not less than 1 in. (25.4 mm) nominal in 
thickness and at least as high as the insulating supports, 
placed on each side of and close to the wiring 

(2) A substantial running board at least Vi in. (12.7 mm) 
thick in back of the conductors with side protections. 
Running boards shall extend at least 1 in. (25.4 mm) 
outside the conductors, but not more than 2 in. (50.8 
mm), and the protecting sides shall be at least 2 in. 
(50.8 mm) high and at least 1 in. (25.4 mm) nominal 
in thickness 



Article 321 — Messenger Supported Wiring 

321-1. Definition. Messenger supported wiring is an ex- 
posed wiring support system using a messenger wire to 
support insulated conductors by any one of the following: 

(1) A messenger with rings and saddles for conductor sup- 
port 

(2) A messenger with a field-installed lashing material for 
conductor support 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-148 



ARTICLE 324 — CONCEALED KNOB-AND-TUBE WIRING 



(3) Factory-assembled aerial cable 

(4) Multiplex cables utilizing a bare conductor, factory as- 
sembled and twisted with one or more insulated con- 
ductors, such as duplex, triplex, or quadruplex type of 
construction 

321-2. Other Articles. Messenger supported wiring shall 
comply with this article and also with the applicable provi- 
sions of other articles in this Code, especially Articles 225 
and 300. 

321-3. Uses Permitted. 

(a) Cable Types. The following shall be permitted to be 
installed in messenger supported wiring under the conditions 
described in the article or section referenced for each: 



321-4. Uses Not Permitted. Messenger supported wiring 
shall not be used in hoistways or where subject to severe 
physical damage. 

321-5. Ampacity. The ampacity shall be determined by 
Section 310-15, 

321-6. Messenger Support. The messenger shall be sup- 
ported at dead ends and at intermediate locations so as to 
eliminate tension on the conductors. The conductors shall 
not be permitted to come into contact with the messenger 
supports or any structural members, walls, or pipes. 

321-7. Grounding. The messenger shall be grounded as 
required by Sections 250-80 and 250-86 for enclosure 
grounding. 



• 



• 



Section 



Metal-clad cable 

Mineral-insulated, metal- 
sheathed cable 

Multiconductor service- 
entrance cable 

Multiconductor underground 
feeder and branch-circuit 
cable 

Other factory-assembled, 
multiconductor control, 
signal, or power cables that 
are identified for the use 

Power and control tray cable 

Power-limited tray cable 



Article 

334 
330 

338 

339 



340 



725-6 1(c) and 
725-7 1(e) 



(b) In Industrial Establishments. In industrial establish- 
ments only, where conditions of maintenance and supervi- 
sion ensure that only qualified persons will service the 
installed messenger supported wiring, the following shall 
be permitted: 

(1) Any of the conductor types shown in Table 310-13 or 
Table 310-62 

(2) MV cable 

Where exposed to weather, conductors shall be listed for 
use in wet locations. Where exposed to direct rays of the 
sun, conductors or cables shall be sunlight resistant. 

(c) Hazardous (Classified) Locations. Messenger sup- 
ported wiring shall be permitted to be used in hazardous 
(classified) locations where the contained cables are permit- 
ted for such use in Sections 501-4, 502-4, 503-3, and 504- 
20. 



321-8. Conductor Splices and Taps. Conductor splices 
and taps made and insulated by approved methods shall be 
permitted in messenger supported wiring. 

Article 324 — Concealed Knob-and-Tube Wiring 

324-1. Definition. Concealed knob-and-tube wiring is a 
wiring method using knobs, tubes, and flexible nonmetallic 
tubing for the protection and support of single insulated 
conductors. 

324-2. Other Articles. Concealed knob-and-tube wiring 
shall comply with this article and also with the applicable 
provisions of other articles in this Code, especially Article 
300. 

324-3. Uses Permitted. Concealed knob-and-tube wiring 
shall be permitted to be installed in the hollow spaces of 
walls and ceilings or in unfinished attics and roof spaces as 
provided in Section 324-11 only as follows: 

(1) For extensions of existing installations, or 

(2) Elsewhere by special permission. 

324-4. Uses Not Permitted. Concealed knob-and-tube wir- 
ing shall not be used in commercial garages, theaters and 
similar locations, motion picture studios, hazardous (classi- 
fied) locations, or in the hollow spaces of walls, ceilings, 
and attics where such spaces are insulated by loose, rolled, 
or foamed-in-place insulating material that envelops the con- 
ductors. 

324-5. Conductors. 

(a) Type. Conductors shall be of a type specified by Article 
310. 



• 



• 



• 



1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 325 — . INTEGRATED GAS SPACER CABLE: TYPE IGS 



70-149 



(b) Ampacity. The ampacity shall be determined by Sec- 
tion 310-15. 

324-6. Conductor Supports. Conductors shall be rigidly 
supported on noncombustible, nonabsorbent insulating ma- 
terials and shall riot contact any other objects. Supports shall 
be installed as follows: 

(1) Within 6 in. (152 mm) of each side of each tap or splice 

(2) At intervals not exceeding 4Vi ft (1.37 m) 

Where it is impracticable to provide supports, conductors 
shall be permitted to be fished through hollow spaces in dry 
locations, provided each conductor is individually enclosed 
in flexible nonmetallic tubing that is in continuous lengths 
between supports, between boxes, or between a support and 
a box. 

324-7. Tie Wires. Where solid knobs are used, conductors 
shall be securely tied thereto by tie wires having insulation 
equivalent to that of the conductor. 

324-8. Conductor Clearances. 

(a) General. A clearance of not less than 3 in. (76 mm) 
shall be maintained between conductors and a clearance of 
not less than 1 in. (25.4 mm) between the conductor and 
the surface over which it passes. 

(b) Limited Conductor Space. Where space is too limited 
to provide these minimum clearances, such as at meters, 
panelboards, outlets, and switch points, the individual con- 
ductors shall be enclosed in flexible nonmetallic tubing, 
which shall be continuous in length between the last support 
and the enclosure or terminal point. 

324-9. Through Walls, Floors, Wood Cross Members, 
etc. Conductors shall comply with Section 320-11 where 
passing through holes in structural members. Where passing 
through wood cross members in plastered partitions, con- 
ductors shall be protected by noncombustible, nonabsorbent, 
insulating tubes extending not less than 3 in. (76 mm) beyond 
the wood meriiber. 

324-10. Clearance from Piping, Exposed Conductors, etc. 

Conductors shall comply with Section 320-12 for clearances 
from other exposed conductors, piping, etc. 

324-11. Unfinished Attics and Roof Spaces. Conductors 
in unfinished attics and roof spaces shall comply with (a) 
or (b). 

FPN: See Section 310-10 for temperature limitation of 
conductors. 



(a) Accessible by Stairway or Permanent Ladder. Con- 
ductors shall be installed along the side of or through bored 
holes in floor joists, studs, or rafters. Where run through 
bored holes, conductors in the joists and in studs or rafters 
to a height of not less than 7 ft (2.13 m) above the floor or 
floor joists shall be protected by substantial running boards 
extending not less than 1 in. (25.4 mm) on each side of the 
conductors. Running boards shall be securely fastened in 
place. Running boards and guard strips shall not be required 
where conductors are installed along the sides of joists, studs, 
or rafters. 

(b) Not Accessible by Stairway or Permanent Ladder. 

Conductors shall be installed along the sides of or through 
bored holes in floor joists, studs, or rafters. 

Exception: In buildings completed before the wiring is in- 
stalled, attic and roof spaces that are not accessible by 
stairway or permanent ladder and have headroom at all 
points less than 3 ft (914 mm), the wiring shall be permitted 
to be installed on the edges of rafters or joists facing the 
attic or roof space. 

324-12. Splices. Splices shall be soldered unless approved 
splicing devices are used. In-line or strain splices shall not 
be used. 

324-13. Boxes. Outlet boxes shall comply with Article 370. 

324-14. Switches. Switches shall comply with Sections 
380-4 and 380- 10(b). 

Article 325 — Integrated Gas Spacer Cable: 
Type IGS 

A. General 

325-1. Definition. Type IGS cable is a factory assembly of 
one or more conductors, each individually insulated and 
enclosed in a loose fit, nonmetallic flexible conduit as an 
integrated gas spacer cable rated through 600 volts. 

325-2. Other Articles. Type IGS cable shall comply with 
this article and also with the applicable provisions of other 
articles in this Code. 

325-3. Uses Permitted. Type IGS cable shall be permitted 
for use underground, including direct burial in the earth, as 
service-entrance conductors, or as feeder or branch-circuit 
conductors. 

325-4. Uses Not Permitted. Type IGS cable shall not be 
used as interior wiring or be exposed in contact with build- 
ings. 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-150 



ARTICLE 326 — MEDIUM VOLTAGE CABLE: TYPE MV 



B. Installation 

325-11. Bending Radius. Where the coilable nonmetallic 
conduit and cable is bent for installation purposes or is flexed 
or bent during shipment or installation, the radii of bends 
measured to the inside of the bend shall not be less than 
specified in Table 325-11. 

Table 325-11. Minimum Radii of Bends 





Minimum Radii 


Conduit Trade 
Size (in.) 






in. 


mm 


2 


24 


610 


3 


35 


889 


4 


45 


1143 



325-21. Insulation. The insulation shall be dry kraft paper 
tapes and a pressurized sulfur hexafluoride gas (SF 6 ), both 
approved for electrical use. The nominal gas pressure shall 
be 20 pounds per square inch gauge (psig) (138 kPa gauge). 
The thickness of the paper spacer shall be as specified 
in Table 325-21. 

Table 325-21. Paper Spacer Thickness 







Thickness 


Size (kcmil) 


in. 


mm 


250-1000 
' 1250-4750 


0.040 
0.060 


1.02 

1.52 



• 



325-12. Bends. A run of Type IGS cable between pull 
boxes or terminations shall not contain more than the equiv- 
alent of four quarter bends (360 degrees total), including 
those bends located immediately at the pull box or termina- 
tions. 

325-13. Fittings. Terminations and splices for Type IGS 
cable shall be identified as a type that is suitable for main- 
taining the gas pressure within the conduit. A valve and cap 
shall be provided for each length of the cable and conduit 
to check the gas pressure or to inject gas into the conduit. 

325-14. Ampacity. The ampacity of Type IGS cable and 
conduit shall not exceed values shown in Table 325-14 for 
single conductor or multiconductor cable. 



325-22. Conduit. The conduit shall be a medium density 
polyethylene identified as suitable for use with natural gas 
rated pipe in 2-in., 3-in., or 4-in. trade size. The percent fill 
dimensions for the conduit are shown in Table 325-22. 

The size of the conduit permitted for each conductor size 
shall be calculated for a percent fill not to exceed those 
found in Table 1, Chapter 9. 

Table 325-22. Conduit Dimensions 



Conduit 

Trade Size 

(in.) 


Outside Diameter 


Inside Diameter 


in. 


mm 


in. 


mm 


2 
3 
4 


2.375 
3.500 
4.500 . 


60 

89 

114 


1.947 
2.886 
3.710 


49.46 
73.30 
94.23 



Table 325-14. Ampacity of Type IGS Cable 



Size (kcmil) 


Amperes 


Size (kcmil) 


Amperes 


250 


119 


2500 


376. 


500 


168 


3000 


412 


750 


206 


3250 


429 


1000 


238 


3500 


445 


1250 


266 


3750 


461 


1500 


292 


4000 


476 


1750 


344 


4250 


491 


2000 


336 


4500 


505 


.2250 


357 


4750 ■ 


519 



C. Construction Specifications 

325-20. Conductors. The conductors shall be solid alumi- 
num rods, laid parallel, consisting of one to nineteen V^-in. 
(12.7-mm) diameter rods. 

The minimum conductor size shall be 250 kcmil and the 
maximum size shall be 4750 kcmil. 



325-24. Marking. The cable shall be marked in accordance 
with Sections 310-1 1(a), 310-1 1(b)(1), and 310-ll(d). 

Article 326 — Medium Voltage Cable: Type MV 

326-1. Definition. Type MV cable is a single or multicon- 
ductor solid dielectric insulated cable rated 2001 volts or 
higher. 

326-2. Other Articles. In addition to the provisions of this 
article, Type MV cable shall comply with the applicable 
provisions of this Code, especially those of Articles 300, 
305, 310, 318, and 490. 

326-3. Uses Permitted. Type MV cables shall be permitted 
for use on power systems rated up to 35,000 volts, nominal, 
in wet or dry locations, in raceways, in cable trays as speci- 
fied in Section 318-3(b)(l) or directly buried in accordance 



• 



1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 328 — FLAT CONDUCTOR CABLE: TYPE FCC 



70-151 



• 



• 



with Section 300-50, and in messenger supported wiring. 

326-4. Uses Not Permitted. Type MV cable shall not be 
used unless identified for the use (1) where exposed to direct 
sunlight, and (2) in cable trays. 

326-5. Construction. Type MV cables shall have copper, 
aluminum, or copper-clad aluminum conductors and shall 
be constructed in accordance with Article 310. 

326-6. Ampacity. The ampacity of Type MV cable shall 
be in accordance with Section 310-60. 

Exception: The ampacity of Type MV cable installed in ca- 
ble tray shall be in accordance with Section 318-13. 

326-7. Marking. Medium voltage cable shall be marked 
as required in Section 310-11. 

Article 328 — Flat Conductor Cable: Type FCC 

A. General 

328-1. Scope. This article covers a field-installed wiring 
system for branch circuits incorporating Type FCC cable 
and associated accessories as defined by the article. The 
wiring system is designed for installation under carpet 
squares. 

328-2. Definitions. 

Type FCC Cable. Type FCC cable consists of three 
or more flat copper conductors placed edge-to-edge and 
separated and enclosed within an insulating assembly. 

FCC System. A complete wiring system for branch cir- 
cuits that is designed for installation under carpet squares. 
The FCC system includes Type FCC cable and associated 
shielding, connectors, terminators, adapters, boxes, and re- 
ceptacles. 

Cable Connector. A connector designed to join Type 
FCC cables without using a junction box. 

Insulating End. An insulator designed to electrically 
insulate the end of a Type FCC cable. 

Top Shield. A grounded metal shield covering under- 
carpet components of the FCC system for the purposes of 
providing protection against physical damage. 

Bottom Shield. A protective layer that is installed be- 
tween the floor and Type FCC flat conductor cable to protect 
the cable from physical damage and may or may not be 
incorporated as an integral part of the cable. 

Transition Assembly. An assembly to facilitate connec- 
tion of the FCC system to other wiring systems, incorporat- 



ing (1) a means of electrical interconnection, and (2) a 
suitable box or covering for providing electrical safety and 
protection against physical damage. 

Metal Shield Connections. Means of connection de- 
signed to electrically and mechanically connect a metal 
shield to another metal shield, to a receptacle housing or 
self-contained device, or to a transition assembly. 

328-3. Other Articles. The FCC systems shall conform 
with the applicable provisions of Articles 210, 220, 240, 
250, and 300. 

328-4. Uses Permitted. 

(a) Branch Circuits. Use of FCC systems shall be permit- 
ted both for general-purpose and appliance branch circuits 
and for individual branch circuits. 

(b) Floors. Use of FCC systems shall be permitted on hard, 
sound, smooth, continuous floor surfaces made of con- 
crete, ceramic, or composition flooring, wood, and similar 
materials. 

(c) Walls. Use of FCC systems shall be permitted on wall 
surfaces in surface metal raceways. 

(d) Damp Locations. Use of FCC systems in damp loca- 
tions shall be permitted. 

(e) Heated Floors. Materials used for floors heated in ex- 
cess of 30°C (86°F) shall be identified as suitable for use at 
these temperatures. 

328-5. Uses Not Permitted. FCC systems shall not be used 
in the following: 

(1) Outdoors or in wet locations 

(2) Where subject to corrosive vapors 

(3) In any hazardous (classified) location 

(4) In residential, school, and hospital buildings 

328-6. Branch-Circuit Ratings. 

(a) Voltage. Voltage between ungrounded conductors shall 
not exceed 300 volts. Voltage between ungrounded conduc- 
tors and the grounded conductor shall not exceed 150 volts. 

(b) Current. General-purpose and appliance branch cir- 
cuits shall have ratings not exceeding 20 amperes. Individual 
branch circuits shall have ratings not exceeding 30 amperes. 

B. Installation 

328-10. Coverings. Floor-mounted Type FCC cable, cable 
connectors, and insulating ends shall be covered with carpet 
squares not larger than 36 in. (914 mm) square. Those carpet 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-152 



ARTICLE 328 — FLAT CONDUCTOR CABLE: TYPE FCC 



squares that are adhered to the floor shall be attached with 
release-type adhesives. 

328-11. Cable Connections and Insulating Ends. All 

Type FCC cable connections shall use connectors identified 
for their use, installed such that electrical continuity, insula- 
tion, and sealing against dampness and liquid spillage are 
provided. All bare cable ends shall be insulated and sealed 
against dampness and liquid spillage, using listed insulating 
ends. 

328-12. Shields. 

(a) Top Shield. A metal top shield shall be installed over all 
floor-mounted Type FCC cable, connectors, and insulating 
ends. The top shield shall completely cover all cable runs, 
corners, connectors, and ends. 

(b) Bottom Shield. A bottom shield shall be installed be- 
neath all Type FCC cable, connectors, and insulating ends. 

328-13. Enclosure and Shield Connections. All metal 
shields, boxes, receptacle housings, and self-contained de- 
vices shall be electrically continuous to the equipment 
grounding conductor of the supplying branch circuit. All 
such electrical connections shall be made with connectors 
identified for this use. The electrical resistivity of such shield 
system shall not be more than that of one conductor of the 
Type FCC cable used in the installation. 

328-14. Receptacles. All receptacles, receptacle housings, 
and self-contained devices used with the FCC system shall 
be identified for this use and shall be connected to the 
Type FCC cable and metal shields. Connection from any 
grounding conductor of the Type FCC cable shall be made 
to the shield system at each receptacle. 

328-15. Connection to Other Systems. Power feed, 
grounding connection, and shield system connection be- 
tween the FCC system and other wiring systems shall be 
accomplished in a transition assembly identified for this use. 

328-16. Anchoring. All FCC system components shall be 
firmly anchored to the floor or wall using an adhesive or 
mechanical anchoring system identified for this use. Floors 
shall be prepared to ensure adherence of the FCC system to 
the floor until the carpet squares are placed. 

328-17. Crossings. Crossings of more than two Type FCC 
cable runs shall not be permitted at any one point. Crossings 
of a Type FCC cable over or under a flat communications 
or signal cable shall be permitted. In each case, a grounded 
layer of metal shielding shall separate the two cables, and 



crossings of more than two flat cables shall not be permitted 
at any one point. 

328-18. System Height. Any portion of an FCC system 
with a height above floor level exceeding 0.090 in. (2.29 
mm) shall be tapered or feathered at the edges to floor level. 

328-19. FCC Systems Alterations. Alterations to FCC 
systems shall be permitted. New cable connectors shall be 
used at new connection points to make alterations. It shall 
be permitted to leave unused cable runs and associated cable 
connectors in place and energized. All cable ends shall be 
covered with insulating ends. 

328-20. Polarization of Connections. All receptacles and 
connections shall be constructed and installed so as to main- 
tain proper polarization of the system. 

C. Construction 

328-30. Type FCC Cable. Type FCC cable shall be listed 
for use with the FCC system and shall consist of three, four, 
or five flat copper conductors, one of which shall be an 
equipment grounding conductor. The insulating material of 
the cable shall be moisture resistant and flame retardant. 

328-31. Markings. Type FCC cable shall be clearly and 
durably marked on both sides at intervals of not more than 
24 in. (610 mm) with the information required by Section 
310-1 1(a) and with the following additional information: 

(1) Material of conductors 

(2) Maximum temperature rating 

(3) Ampacity 

328-32. Conductor Identification. 

(a) Colors. Conductors shall be clearly and durably marked 
on both sides throughout their length as specified in Section 
310-12. 

(b) Order. For a 2-wire FCC system with grounding, the 
grounding conductor shall be central. 

328-33. Corrosion Resistance. Metal components of the 
system shall be either corrosion resistant, coated with corro- 
sion-resistant materials, or insulated from contact with cor- 
rosive substances. 

328-34. Insulation. All insulating materials in the FCC 
systems shall be identified for their use. 

328-35. Shields. 

(a) Materials and Dimensions. All top and bottom shields 
shall be of designs and materials identified for their use. 



• 



• 



• 



1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 330 — MINERAL-INSULATED, METAL-SHEATHED CABLE: TYPE MI 



70-153 



Top shields shall be metal. Both metallic and nonmetallic 
materials shall be permitted for bottom shields. 

(b) Resistivity. Metal shields shall have cross-sectional 
areas that provide for electrical resistivity of not more than 
that of one conductor of the Type FCC cable used in the 
installation. 

(c) Metal-Shield Connectors. Metal shields shall be con- 
nected to each other and to boxes, receptacle housings, 
self-contained devices, and transition assemblies using 
metal-shield connectors. 

328-36. Receptacles and Housings. Receptacle housings 
and self-contained devices designed either for floor mount- 
ing or for in- or on-wall mounting shall be permitted for 
use with the FCC system. Receptacle housings and self- 
contained devices shall incorporate means for facilitating 
entry and termination of Type FCC cable and for electrically 
connecting the housing or device with the metal shield. 
Receptacles and self-contained devices shall comply with 
Section 210-7. Power and communications outlets installed 
together in common housing shall be permitted in accor- 
dance with Section 800-52(a)(2), Exception No. 1. 

328-37. Transition Assemblies. All transition assemblies 
shall be identified for their use. Each assembly shall incor- 
porate means for facilitating entry of the Type FCC cable 
into the assembly, for connecting the Type FCC cable to 
grounded conductors, and for electrically connecting the 
assembly to the metal cable shields and to equipment ground- 
ing conductors. 

Article 330 — Mineral-Insulated, Metal-Sheathed 
Cable: Type MI 

A. General 

330-1. Definition. Type MI mineral-insulated, metal- 
sheathed cable is a factory assembly of one or more conduc- 
tors insulated with a highly compressed refractory mineral 
insulation and enclosed in a liquidtight and gastight contin- 
uous copper or alloy steel sheath. 

330-2. Other Articles. Type MI cable shall comply with 
this article and also with the applicable provisions of other 
articles in this Code, especially Article 300. 

330-3. Uses Permitted. Type MI cable shall be permitted 
as follows: 

(1) For services, feeders, and branch circuits 

(2) For power, lighting, control, and signal circuits 

(3) In dry, wet, or continuously moist locations 



(4) Indoors or outdoors 

(5) Where exposed or concealed 

(6) Embedded in plaster, concrete, fill, or other masonry, 
whether above or below grade 

(7) In any hazardous (classified) location 

(8) Where exposed to oil and gasoline 

(9) Where exposed to corrosive conditions not deteriorat- 
ing to its sheath 

(10) In underground runs where suitably protected against 
physical damage and corrosive conditions 

330-4. Uses Not Permitted. Type MI cable shall not be 
used where exposed to destructive corrosive conditions, un- 
less protected by materials suitable for the conditions. 

B. Installation 

330-10. Wet Locations. Where installed in wet locations, 
Type MI cable shall comply with Section 300-6(c). 

330-11. Through Joists, Studs, or Rafters. Type MI cable 
shall comply with Section 300-4 where installed through 
studs, joists, rafters, or similar wood members. 

330-12. Supports. Type MI cable shall be supported by 
one of the following means: 

(1) Supported securely at intervals not exceeding 6 ft 
(1.83 m) by straps, staples, hangers, or similar fittings 
designed and installed so as not to damage the cable 

Exception: Where cable is fished, support shall not be re- 
quired. 

(2) Supported in accordance with Section 318-8(b) where 
installed in cable trays 

330-13. Bends. Bends in Type MI cable shall be made so 
as not to damage the cable. The radius of the inner edge of 
any bend shall not be less than shown as follows: 

(1) Five times the external diameter of the metallic sheath 
for cable not more than 3 A in. (19 mm) in external 
diameter 

(2) Ten times the external diameter of the metallic sheath 
for cable greater than 3 /4 in. (19 mm) but not more than 
1 in. (25.4 mm) in external diameter 

330-14. Fittings. Fittings used for connecting Type MI 
cable to boxes, cabinets, or other equipment shall be identi- 
fied for such use. Where single-conductor cables enter fer- 
rous metal boxes or cabinets, the installation shall comply 
with Section 300-20 to prevent inductive heating. 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-154 



ARTICLE 331 —ELECTRICAL NONMETALLIC TUBING 



330-15. Terminal Seals. Where Type MI cable terminates, 
a seal shall be provided immediately after stripping to pre- 
vent the entrance of moisture into the insulation. The conduc- 
tors extending beyond the sheath shall be individually 
provided with an insulating material. 

330-16. Single Conductors. Where single-conductor ca- 
bles are used, all phase conductors and, where used, the 
neutral conductor shall be grouped together to minimize 
induced voltage on the sheath. Where single-conductor ca- 
bles enter ferrous enclosures, the installation shall comply 
with Section 300-20 to prevent heating from induction. 



C. Construction Specifications 

330-20. Conductors. Type MI cable conductors shall be 
of solid copper or nickel-clad copper with a resistance corre- 
sponding to standard AWG sizes. 

330-21. Insulation. The conductor insulation in Type MI 
cable shall be a highly compressed refractory mineral that 
provides proper spacing for all conductors. 

330-22. Outer Sheath. The outer sheath shall be of a con- 
tinuous construction to provide mechanical protection and 
moisture seal. Where made of copper, it shall provide an 
adequate path for equipment grounding purposes. Where 
made of steel, an equipment grounding conductor in accor- 
dance with Article 250 shall be provided. 



Article 331 — Electrical Nonmetallic Tubing 

A. General 

331-1. Definition. Electrical nonmetallic tubing is a pli- 
able corrugated raceway of circular cross section with inte- 
gral or associated couplings, connectors, and fittings listed 
for the installation of electric conductors. It is composed of 
a material that is resistant to moisture and chemical atmo- 
spheres and is flame retardant. 

A pliable raceway is a raceway that can be bent by hand 
with a reasonable force, but without other assistance, 

Electrical nonmetallic tubing shall be made of material 
that does not exceed the ignitibility, flammability, smoke 
generation, and toxicity characteristics of rigid (nonplasti- 
cized) polyvinyl chloride. 

331-2. Other Articles. Installations for electrical nonme- 
tallic tubing shall comply with the provisions of the applica- 
ble sections of Article 300. Where equipment grounding is 
required by Article 250, a separate equipment grounding 
conductor shall be installed in the raceway. 



331-3. Uses Permitted. The use of electrical nonmetallic 
tubing and fittings shall be permitted in the following: 

(1) In any building not exceeding three floors above grade 

(a) For. exposed work, where not subject to physical 
damage 

(b) Concealed within walls, floors, and ceilings 

FPN: See Section 336-5(a)(l) for definition of first floor. 

(2) In any building exceeding three floors above grade, 
electrical nonmetallic tubing shall be concealed within 
walls, floors, and ceilings where the walls, floors, and 
ceilings provide a thermal barrier of material that has 
at least a 15-minute finish rating as identified in listings 
of fire-rated assemblies. The 15-minute finish rated ther- 
mal barrier shall be permitted to be used for combustible 
walls, floors, and ceilings. 

FPN: A finish rating is established for assemblies containing 
combustible (wood) supports. The finish rating is defined 
as the time at which the wood stud or wood joist reaches 
an average temperature rise of 121°C (250°F) or an individual 
temperature of 163°C (325°F) as measured on the plane of 
the wood nearest the fire. A finish rating is not intended to 
represent a rating for a membrane ceiling. 

(3) In locations subject to severe corrosive influences as 
covered in Section 300-6 and where subject to chemicals 
for which the materials are specifically approved 

(4) In concealed, dry, and damp locations not prohibited by 
Section 331-4 

(5) Above suspended ceilings where the suspended ceilings 
provide a thermal barrier of material that has at least a 
15-minute finish rating as identified in listings of fire- 
rated assemblies, except as permitted in Section 331- 
3(l)(a). 

(6) Encased in poured concrete, or embedded in a concrete 
slab on grade where ENT is placed on sand or approved 
screenings, provided fittings identified for this purpose 
are used for connections 

(7) For wet locations indoors as permitted in this section 
or in a concrete slab on or below grade, with fittings 
listed for the purpose 

(8) Vi in. through 1 in. as listed manufactured prewired 
assembly 

FPN: Extreme cold may cause some types of nonmetallic 
conduits to become brittle and, therefore, more susceptible 
to damage from physical contact. 

331-4. Uses Not Permitted. Electrical nonmetallic tubing 
shall not be used in the following: 

(1) In hazardous (classified) locations, except as permitted 
by Section 504-20 and Section 505-15(a)(l) 



• 



• 



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1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 333 — ARMORED CABLE: TYPE AC 



70-155 



(2) For the support of fixtures and other equipment 

(3) Where subject to ambient temperatures in excess of 50°C 
(122°F) unless listed otherwise 

(4) For conductors whose insulation temperature limitations 
would exceed those for which the tubing is listed 

(5) For direct earth burial 

(6) Where the voltage is over 600 volts 

(7) In exposed locations, except as permitted by Sections 
331-3(1), 331-3(5), and 331-3(7) 

(8) In theaters and similar locations, except as provided in 
Articles 518 and 520 

(9) Where exposed to the direct rays of the sun, unless 
identified as sunlight resistant 



and shall be secured at intervals not exceeding 3 ft (914 mm) 
or, for horizontal runs, it shall be permitted to be supported 
by openings in framing members at intervals not exceeding 
3 ft (914 mm). In addition, it shall be securely fastened 
in place within 3 ft (914 mm) of each outlet box, device 
box, junction box, cabinet, or fitting where it terminates. 

Exception: Lengths not exceeding a distance of 6 ft (1.83 m) 
from a fixture terminal connection for tap connections to 
lighting fixtures shall be permitted without being secured. 

331-12. Boxes and Fittings. Electrical nonmetallic tubing 
shall be used only with listed fittings. Boxes and fittings 
shall comply with the applicable provisions of Article 370. 



B. Installation 
331-5. Size. 

(a) Minimum. Tubing smaller than V^-in. electrical trade 
size shall not be used. 

(b) Maximum. Tubing larger than 2-in. electrical trade size 
shall not be used. 

FPN: Metric trade numerical designations for electrical rton- 
metallic tubing are Vi = 16, Va = 21, 1 = 27, VA ■= 35, 
l'/ 2 = 41, and 2 = 53. 

331-6. Number of Conductors in Tubing. The number of 
conductors in a single tubing shall not exceed that permitted 
by the percentage fill in Table 1, Chapter 9. 

331-7. Trimming. All cut ends of tubing shall be trimmed 
inside and outside to remove rough edges. 

331-8. Joints. All joints between lengths of tubing and be- 
tween tubing and couplings, fittings, and boxes shall be by 
an approved method. 

331-9. Bends — How Made. Bends of electrical nonme- 
tallic tubing shall be made so that the tubing will not be 
damaged and that the internal diameter of the tubing will 
not be effectively reduced. Bends shall be permitted to be 
made manually without auxiliary equipment, and the radius 
of the curve of the inner edge of such bends shall not be 
less than shown in Table 346-10. 



331-13. Splices and Taps. Splices and taps shall be made 
only injunction boxes, outlet boxes, device boxes, or conduit 
bodies. See Article 370 for rules on the installation and use 
of boxes and conduit bodies. 

331-14. Bushings. Where a tubing enters a box, fitting, or 
other enclosure, a bushing or adapter shall be provided to 
protect the wire from abrasion unless the box, fitting, or 
enclosure design provides equivalent protection. 

FPN: See Section 300-4(f) for the protection of conductors 
size No. 4 or larger. 



C. Construction Specifications 

331-15. General. Electrical nonmetallic tubing shall be 
clearly and durably marked at least every 10 ft (3.05 m) as 
required in the first sentence of Section 110-21. The type 
of material shall also be included in the marking. Tubing 
that has limited smoke-producing characteristics shall be 
permitted to be identified with the suffix LS. The type, size, 
and quantity of conductors used in prewired manufactured 
assemblies shall be identified by means of a printed tag or 
label attached to each end of the manufactured assembly 
and either the carton, coil, or reel. The enclosed conductors 
shall be marked in accordance with Section 310-11. 

ENT, as a prewired manufactured assembly, shall be pro- 
vided in continuous lengths capable of being shipped in a 
coil, reel, or carton without damage. 



331-10. Bends — Number in One Run. There shall not 
be more than the equivalent of four quarter bends (360 
degrees total) between pull points, e.g., conduit bodies and 
boxes. 

331-11. Supports. Electrical nonmetallic tubing shall be 
installed as a complete system as provided in Article 300 



Article 333 — Armored Cable: Type AC 

A. General 

333-1. Definition. Type AC cable is a fabricated assembly 
of insulated conductors in a flexible metallic enclosure. See 
Section 333-19. 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-156 



ARTICLE 333 — ARMORED CABLE: TYPE AC 



333-2. Other Articles. Type AC cable shall comply with 
this article and also with the applicable provisions of other 
articles in this Code, especially Article 300. 

333-3. Uses Permitted. Except where otherwise specified 
in this Code and where not subject to physical damage, Type 
AC cable shall be permitted for branch circuits and feeders 
in both exposed and concealed work and in cable trays where 
identified for such use. 

Type AC cable shall be permitted in dry locations and 
embedded in plaster finish on brick or other masonry, except 
in damp or wet locations. It shall be permissible to run or 
fish this cable in the air voids of masonry block or tile walls 
where such walls are not exposed or subject to excessive 
moisture or dampness. 

333-4. Uses Not Permitted. Type AC cable shall not be 
used where prohibited elsewhere in this Code, including the 
following: 

(1) In theaters and similar locations, except as provided in 
Article 518, Places of Assembly 

(2) In motion picture studios 

(3) In any hazardous (classified) location except as permit- 
ted by Sections 501 -4(b), Exception, 502-4(b), Excep- 
tion No. 1, and 504-20 

(4) Where exposed to corrosive fumes or vapors 

(5) On cranes or hoists, except as provided in Section 610- 
11(c) 

(6) In storage battery rooms 

(7) In hoistways or on elevators, except as provided in Sec- 
tion 620-21 

(8) In commercial, garages where prohibited in Article 511 

B. Installation 

333-7. Support. Type AC cable shall be secured by staples, 
cable ties, straps, hangers, or similar fittings designed and 
installed so as not to damage the cable at intervals not 
exceeding AVi ft (1.37 m) and within 12 in. (305 mm) of 
every outlet box, junction box, cabinet, or fitting. 

(a) Horizontal Runs. Type AC cable installed in other than 
vertical runs through bored or punched holes in wood or 
metal framing members, or through notches in wooden fram- 
ing members and protected by a steel plate at least '/i6 in. 
(1.59 mm) thick, shall be considered secured where the 
support intervals do not exceed AVi ft (1.37 m) and the 
armored cable is securely fastened in place by an approved 
means within 12 in. (505 mm) of each box, cabinet, conduit 
body, or other armored cable termination. 

(b) Unsupported. Type AC cable shall be permitted to be 
unsupported where the cable is 



(1) Fished between access points, where concealed in fin- 
ished buildings or structures and supporting is impracti- 
cable; 

(2) Not more than 2 ft (610 mm) in length at terminals 
where flexibility is necessary; or 

(3) Not more than 6 ft (1.83 m) in length from an outlet 
for connections within an accessible ceiling to lighting 
fixtures or equipment. 

(c) Cable Tray Installations. Type AC cable installed in 
cable trays shall comply with Section 318-8(b). 

333-8. Bending Radius. All bends shall be made so that 
the cable will not be damaged, and the radius of the curve 
of the inner edge of any bend shall not be less than five 
times the diameter of the Type AC cable. 

333-9. Boxes and Fittings. At all points where the armor 
of AC cable terminates, a fitting shall be provided to protect 
wires from abrasion, unless the design of the outlet boxes 
or fittings is suoh as to afford equivalent protection, and, in 
addition, an insulating bushing or its equivalent protection 
shall be provided between the conductors and the armor. 
The connector or clamp by which the Type AC cable is 
fastened to boxes or cabinets shall be of such design that 
the insulating bushing or its equivalent will be visible for 
inspection. Where change is made from Type AC cable to 
other cable or raceway wiring methods, a box, fitting, or 
conduit body shall be installed at junction points as required 
in Section 300-15. 

333-10. Through or Parallel to Framing Members. Type 
AC cable shall comply with Section 300-4 where installed 
through or parallel to studs, joists, rafters, or similar wood 
or metal members. 

333-11. Exposed Work. Exposed runs of cable shall 
closely follow the surface of the building finish or of running 
boards. Exposed runs shall also be permitted to be installed 
on the underside of joists where supported at each joist and 
located so as not to be subject to physical damage. 

333-12. In Accessible Attics. Type AC cables in accessible 
attics or roof spaces shall be installed as specified in (a) and 
(b). 

(a) Where Run Across the Top of Floor Joists. Where 
run across the top of floor joists, or within 7 ft (2.13 m) of 
floor or floor joists across the face of rafters or studding, in 
attics and roof spaces that are accessible, the cable shall be 
protected by substantial guard strips that are at least as high 
as the cable. Where this space is not accessible by permanent 
stairs or ladders, protection shall only be required within 



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1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 334 — METAL-CLAD CABLE: TYPE MC 



70-157 



6 ft (1.83 m) of the nearest edge of the scuttle hole or attic 
entrance. 

(b) Cable Installed Parallel to Framing Members. 

Where the cable is installed parallel to the sides of rafters, 
studs, or floor joists, neither guard strips nor running boards 
shall be required, and the installation shall also comply with 
Section 300-4(d). 



C. Construction Specifications 

333-19. Construction. Type AC cable shall have an armor 
of flexible metal tape. The insulated conductors shall be in 
accordance with Section 333-20. Cables of the AC type shall 
have an internal bonding strip of copper or aluminum in 
intimate contact with the armor for its entire length. 

333-20. Conductors. Insulated conductors shall be of a 
type listed in Table 310-13 or those identified for use in 
this cable. In addition, the conductors shall have an overall 
moisture-resistant and fire-retardant fibrous covering. For 
Type ACT, a moisture-resistant fibrous covering shall be 
required only on the individual conductors. The ampacity 
shall be determined by Section 310-15. 

Armored cable installed in thermal insulation shall have 
conductors rated at 90°C (194°F). The ampacity of cable 
installed in these applications shall be that of 60°C (140°F) 
conductors. 

333-21. Grounding. Type AC cable shall provide an ade- 
quate path for equipment grounding as required by Section 
250-2(d). 

333-22. Marking. The cable shall be marked in accordance 
with Section 310-11, except that Type AC shall have ready 
identification of the manufacturer by distinctive external 
markings on the cable sheath throughout its entire length. 



Article 334 — Metal-Clad Cable: type MC 

A. General 

334-1. Definition. Type MC cable is a factory assembly of 
one or more insulated circuit conductors with or without 
optical fiber members enclosed in an armor of interlocking 
metal tape, or a smooth or corrugated metallic sheath. 

334-2. Other Articles. Metal-clad cable shall comply with 
this article and also with the applicable provisions of other 
articles in this Code, especially Article 300. 

Type MC cable shall be permitted for systems in excess 
of 600 volts, nominal. See Section 300-2(a). 



334-3. Uses Permitted. Unless specifically prohibited 
elsewhere in this Code and where not subject to physical 
damage, Type MC cables shall be permitted as follows: 

(1) For services, feeders, and branch circuits 

(2) For power, lighting, control, and signal circuits 

(3) Indoors or outdoors 

(4) Where exposed or concealed 

(5) Direct buried where identified for such use 

(6) In cable tray 

(7) In any raceway 

(8) As open runs of cable 

(9) As aerial cable on a messenger 

(10) In hazardous (classified) locations as permitted in Arti- 
cles 501, 502, 503, 504, and 505 

(11) In dry locations and embedded in plaster finish on 
brick or other masonry except in damp or wet locations 

(12) In wet locations where any of the following conditions 
are met: 

(a) The metallic covering is impervious to moisture. 

(b) A lead sheath or moisture-impervious jacket is pro- 
vided under the metal covering. 

(c) The insulated conductors under the metallic cov- 
ering are listed for use in wet locations. 

334-4. Uses Not Permitted. Type MC cable shall not be 
used where exposed to destructive corrosive conditions, such 
as direct burial in the earth, in concrete, or where exposed 
to cinder fills, strong chlorides, caustic alkalis, or vapors of 
chlorine or of hydrochloric acids, unless the metallic sheath 
is suitable for the conditions or is protected by material 
suitable for the conditions. 

B. Installation 

334-10. Installation. Type MC cable shall be installed in 
compliance with Articles 300, 490, 725, and Section 770- 
52 as applicable and in accordance with the following. 

(a) Supported Cables. Type MC cable shall be supported 
and secured at intervals not exceeding 6 ft (1.83 m). Cables 
containing four or fewer conductors, sized no larger than 
NO. 10 shall be secured within 12 in. (305 mm) of every 
box, cabinet, fitting, or other cable termination. 

(1) Horizontal Runs. Cables installed in other than ver- 
tical runs through bored or punched holes in wood or metal 
framing members, or through notches in wooden framing 
members and protected by a steel plate at least '/i6 in. 
(1.59 mm) thick shall be considered supported and secured 
where such support does not exceed 6-ft (1.83-m) intervals. 

(2) At Terminations. Cables containing four or fewer 
conductors, sized not larger than No. 10 shall be secured 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-158 



ARTICLE 334 — METAL-CLAD CABLE: TYPE MC 



within 12 in. (305 mm) of every box, cabinet, fitting, or 
other cable termination. 

(b) Unsupported Cables. Type MC cable shall not be re- 
quired to be supported and secured where the cable is fished 
between access points, where concealed in finished buildings 
or structures and supporting is impracticable, or where used 
in lengths not more than 6 ft (1.83 m) from an outlet for 
connections within an accessible ceiling to lighting fixture(s) 
or equipment. 

(c) Cable Tray. Type MC cable installed in cable tray shall 
comply with Article 318. 

(d) Direct Buried. Direct-buried cable shall comply with 
Sections 300-5 or 300-50, as appropriate. 

(e) Installed as Service-Entrance Cable. Type MC cable 
installed as service-entrance cable shall comply with Article 
230. 

(f) Installed Outside of Buildings or as Aerial Ca- 
ble. Type MC cable installed outside of buildings or as 
aerial cable shall comply with Article 225 and Article 321. 

(g) Through or Parallel to Joists, Studs, and Rafters. 

Type MC cable shall comply with Section 300-4 where 
installed through or parallel to joists, studs, rafters, or similar 
wood or metal members. 

(h) In Accessible Attics. The installation of Type MC cable 
in accessible attics or roof spaces shall also comply with 
Section 333-12. 

334-11. Bending Radius. All bends shall be made so that 
the cable will not be damaged, and the radius of the curve 
of the inner edge of any bend shall not be less than shown 
in (a) through (c). 

(a) Smooth Sheath. 

(1) Ten times the external diameter of the metallic sheath 
for cable not more than Va in. (19 mm) in external diameter 

(2) Twelve times the external diameter of the metallic 
sheath for cable more than 3 A in. (19 mm) but not more than 
11/2 in. (38 mm) in external diameter 

(3) Fifteen times the external diameter of the metallic 
sheath for cable more than VA in. (38 mm) in external 
diameter 

(b) Interlocked-Type Armor or Corrugated Sheath. 

Seven times the external diameter of the metallic sheath. 

(c) Shielded Conductors. Twelve times the overall diam- 
eter of one of the individual conductors or seven times the 
overall diameter of the multiconductor cable, whichever is 
greater. 



334-12. Fittings. Fittings used for connecting Type MC 
cable to boxes, cabinets, or other equipment shall be listed 
and identified for such use. Where single-conductor cables 
enter ferrous metal boxes or cabinets, the installation shall 
comply with Section 300-20 to prevent inductive heating. 

334-13. Ampacity. The ampacity of Type MC cable shall 
be in accordance with Sections 310-15 or 310-60. 

Exception No. 1: The ampacities for Type MC cable in- 
stalled in cable tray shall be determined in accordance with 
Sections 318-11 and 318-13. 

Exception No. 2: The ampacities of No. 18 and No. 16 
conductors shall be in accordance with Table 402-5. 

FPN: See Section 3 10- 10 for temperature limitation of con- 
ductors. 



C. Construction Specifications 

334-20. Conductors. The conductors shall be of copper, 
aluminum, or copper-clad aluminum, solid or stranded. 

The minimum conductor size shall be No. 18 copper and 
No. 12 aluminum or copper-clad aluminum. 

334-21. Insulation. The insulated conductors shall comply 
with (a) or (b). 

(a) 600 Volts. Insulated conductors in sizes No. 18 and No. 
16 shall be of a type listed in Table 402-3, with a maximum 
operating temperature not less than 90°C (194°F), and as 
permitted by Section 725-27. Conductors larger than No. 16 
shall be of a type listed in Table 3 1 0- 1 3 or of a type identified 
for use in Type MC cable. 

(b) Over 600 Volts. Insulated conductors shall be of a type 
listed in Tables 310-61 through 310-64. 

334-22. Metallic Sheath. The metallic covering shall be 
one of the following types: smooth metallic sheath, corru- 
gated metallic sheath, interlocking metal tape armor. The 
metallic sheath shall be continuous and close fitting. 

Supplemental protection of an outer covering of corro- 
sion-resistant material shall be permitted and shall be re- 
quired where such protection is needed. The sheath shall 
not be used as a current-carrying conductor. 

FPN: See Section 300-6 for protection against corrosion. 

334-23. Grounding. Type MC cable shall provide an ade- 
quate path for equipment grounding as required by Article 
250. 

334-24. Marking. The cable shall be marked in accordance 
with Section 310-11. 



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1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 336 — NONMETALLIC-SHEATHED CABLE: TYPES NM, NMC, AND NMS 



70-159 



• 



Article 336 — Nonmetallic-Sheathed Cable: 
Types NM, NMC, and NMS 

336-1. Scope. This article covers the use, installation, and 
construction specifications of nonmetallic-sheathed cable. 

A. General 

336-2. Definition. Nonmetallic-sheathed cable is a factory 
assembly of two or more insulated conductors having an 
outer sheath of moisture-resistant, flame-retardant, nonme- 
tallic material. 

336-3. Other Articles. Installations of nonmetallic- 
sheathed cable shall comply with the other applicable provi- 
sions of this Code, especially Articles 300 and 310. 

336-4. Uses Permitted. Type NM, Type NMC, and Type 
NMS cables shall be permitted to be used in the following: 

(1) One- and two-family dwellings 

(2) Multifamily dwellings and other structures, except as 
prohibited in Section 336-5 

(3) Cable trays, where the cables are identified for the use 

FPN: See Section 310-10 for temperature limitation of con- 
ductors. 

(a) Type NM. Type NM cable shall be permitted for both 
exposed and concealed work in normally dry locations. It 
shall be permissible to install or fish Type NM cable in air 
voids in masonry block or tile walls where such walls are 
not exposed or subject to excessive moisture or dampness. 

(b) Type NMC. Type NMC cable shall be permitted as 
follows: 

(1) For both exposed and concealed work in dry, moist, 
damp, or corrosive locations 

(2) In outside and inside walls of masonry block or tile 

(3) In a shallow chase in masonry, concrete, or adobe pro- 
tected against nails or screws by a steel plate at least 
Vi6-in. (1.59-mm) thick, and covered with plaster, adobe, 
or similar finish 

(c) Type NMS. Type NMS cable shall be permitted for 
both exposed and concealed work in normally dry locations. 
It shall be permissible to install or fish Type NMS cable in 
air voids in masonry block or tile walls where such walls 
are not exposed or subject to excessive moisture or damp- 
ness. Type NMS cable shall be used as permitted in Article 
780. 

336-5. Uses Not Permitted. 

(a) Types NM, NMC, and NMS. Types NM, NMC, and 
NMS cables shall not be used in the following: 



(1) In any multifamily dwelling or other structure exceeding 
three floors above grade 

For the purpose of this article, the first floor of a building 
shall be that floor that has 50 percent or more of the exterior 
wall surface area level with or above finished grade. One 
additional level that is the first level and not designed for 
human habitation and used only for vehicle parking, storage, 
or similar use shall be permitted. 

(2) As service-entrance cable 

(3) In commercial garages having hazardous (classified) lo- 
cations as provided in Section 511-3 

(4) In theaters and similar locations, except as provided in 
Article 518, Places of Assembly 

(5) In motion picture studios 

(6) In storage battery rooms 

(7) In hoistways 

(8) Embedded in poured cement, concrete, or aggregate 

(9) In any hazardous (classified) location, except as permit- 
ted by Sections 501-4(b), Exception, 502-4(b), Excep- 
tion, and 504-20 

(b) Types NM and NMS. Types NM and NMS cable shall 
not be installed in the following: 

(1) Where exposed to corrosive fumes or vapors 

(2) Where embedded in masonry, concrete, adobe, fill, or 
plaster 

(3) In a shallow chase in masonry, concrete, or adobe and 
covered with plaster, adobe, or similar finish 

B. Installation 

336-6. Exposed Work — General. In exposed work, ex- 
cept as provided in Section 300-1 1(a), the cable shall be 
installed as specified in (a) through (d). 

(a) To Follow Surface. The cable shall closely follow the 
surface of the building finish or of running boards. 

(b) Protection from Physical Damage. The cable shall be 
protected from physical damage where necessary by conduit, 
electrical metallic tubing, Schedule 80 PVC rigid non- 
metallic conduit, pipe, guard strips, listed surface metal or 
nonmetallic raceway, or other means. Where passing through 
a floor, the cable shall be enclosed in rigid metal conduit, 
intermediate metal conduit, electrical metallic tubing, Sched- 
ule 80 PVC rigid nonmetallic conduit, listed surface metal 
or nonmetallic raceway, or other metal pipe extending at 
least 6 in. (152 mm) above the floor. 

(c) In Unfinished Basements. Where the cable is run at 
angles with joists in unfinished basements, it shall be per- 
missible to secure cables not smaller than two No. 6 or three 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-160 



ARTICLE 336 — NONMETALLIC-SHEATHED CABLE: TYPES NM, NMC, AND NMS 



No. 8 conductors directly to the lower edges of the joists. 
Smaller cables shall either be run through bored holes in 
joists or on running boards. 

(d) In Accessible Attics. The installation of cable in acces- 
sible attics or roof spaces shall also comply with Section 
333-12. 

336-9. Through or Parallel to Framing Members. Types 
NM, NMC, or NMS cable shall comply with Section 300-4 
where installed through or parallel to joists, studs, rafters, 
or similar wood or metal members. 

336-16. Bends. Bends in cable shall be made so, and other 
handling shall be such, that the cable will not be damaged 
and the radius of the curve of the inner edge of any bend 
shall not be less than five times the diameter of the cable. 

336-18. Supports. Nonmetallic-sheathed cable shall be se- 
cured by staples, cable ties, straps, or similar fittings de- 
signed and installed so as not to damage the cable. Cable 
shall be secured in place at intervals not exceeding 4 l A ft 
(1.37 m) and within 12 in. (305 mm) from every cabinet, 
box, or fitting. Flat cables shall not be stapled on edge. 
Cables run through holes in wood or metal joists, rafters, 
or studs shall be considered to be supported and secured. 

FPN: See Section 370- 17(c) for support where nonmetallic 
boxes are used. 

Exception No. 1: For concealed work in finished buildings 
or finished panels for prefabricated buildings where such 
supporting is impracticable, it shall be permissible to fish 
cable between access points. 

Exception No: 2: A wiring device identified for the use, 
without a separate outlet box, incorporating an integral 
cable clamp shall be permitted where the cable is secured 
in place at intervals not exceeding 4 l hft (1.37 m) and within 
12 in. (305 mm) from the wiring device wall opening, and 
there shall be at least a 12-in. (305-mm) loop of unbroken 
cable or 6 in. (152 mm) of a cable end available on the 
interior side of the finished wall to permit replacement. 

Exception No. 3: Lengths not more than 4 l h ft (1.37 m) 
from an outlet for connection within an accessible ceiling 
to lighting fixture(s) or equipment. 

336-20. Boxes of Insulating Material. Nonmetallic outlet 
boxes shall be permitted as provided in Section 370-3. 

336-21. Devices of Insulating Material. Switch, outlet, 
and tap devices of insulating material shall be permitted to 
be used without boxes in exposed cable wiring and for 
rewiring in existing buildings where the cable is concealed 
and fished. Openings in such devices shall form a close fit 
around the outer covering of the cable and the device shall 



fully enclose the part of the cable from which any part of 
the covering has been removed. 

Where connections to conductors are by binding-screw 
terminals, there shall be available as many terminals as 
conductors. 

336-25. Devices with Integral Enclosures. Wiring devices 
with integral enclosures identified for such use shall be 
permitted as provided in Section 300- 15(e). 

336-26. Ampacity. The ampacity of Types NM, NMC, and 
NMS cable shall be that of 60°C (140°F) conductors and 
shall comply with Section 310-15. 

The 90°C (194°F) rating shall be permitted to be used 
for ampacity derating purposes provided the final derated 
ampacity does not exceed that for a 60°C (140°F) rated 
conductor. 



C. Construction Specifications 

336-30. General. Nonmetallic-sheathed cable shall com- 
ply with (a) and (b). 

(a) Construction. The outer cable sheath shall be a non- 
metallic material. 

(1) Type NM. The overall covering shall be flame re- 
tardant and moisture resistant. 

(2) Type NMC. The overall covering shall be flame 
retardant, moisture resistant, fungus resistant, and corrosion 
resistant. 

(3) Type NMS. Type NMS cable is a factory assembly 
of insulated power, communications, and signaling conduc- 
tors enclosed within a common sheath of moisture-resistant, 
flame-retardant, nonmetallic material. The sheath shall be 
applied so as to separate the power conductors from the 
communications and signaling conductors. The signaling 
conductors shall be permitted to be shielded. An optional 
outer jacket shall be permitted. 

FPN: For composite optical cable, see Sections 770-4 and 
770-52. 

(b) Conductors. The insulated power conductors shall be 
one of the types listed in Table 310-13 that is suitable for 
branch-circuit wiring or one that is identified for use in these 
cables. 

The power conductors shall be sizes No. 14 through 
No. 2 with copper conductors or sizes No. 12 through No. 2 
with aluminum or copper-clad aluminum conductors. 

The signaling conductors shall comply with Section 
780-5. 

In addition to the insulated conductors, the cable shall 
be permitted to have an insulated or bare conductor for 



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1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 338 — SERVICE-ENTRANCE CABLE: TYPES SE AND USE 



70-161 



equipment grounding purposes only. Where provided, the 
grounding conductor shall be sized in accordance with Arti- 
cle 250. 

Conductors shall be rated at 90°C (194°F). 

FPN: Types NM, NMC, and NMS cable identified by the 
markings NM-B, NMC-B, and NMS-B meet this require- 
ment. 



336-31. Marking. The cable shall be marked in accordance 
with Section 310-11. 



(b) Grounded Conductor Not Insulated. Type SE ser- 
vice-entrance cables without individual insulation on the 
grounded circuit conductor shall not be used as a branch 
circuit or as a feeder within a building, except a cable that 
has a final nonmetallic outer covering and is supplied by 
alternating current at not over 150 volts to ground shall be 
permitted as a feeder to supply only other buildings on the 
same premises. 

Type SE service-entrance cable shall be permitted for use 
where the fully insulated conductors are used for circuit 
wiring and the uninsulated conductor is used for equipment 
grounding purposes. 



Article 338 — Service-Entrance Cable: Types SE 
and USE 

338-1. Definition. Service-entrance cable is a single con- 
ductor or multiconductor assembly provided with or without 
an overall covering, primarily used for services, and is of 
the following types. 

(a) Type SE. Type SE, having a flame-retardant, moisture- 
resistant covering. 

(b) Type USE. Type USE, identified for underground use, 
having a moisture-resistant covering, but not required to 
have a flame-retardant covering. 

Cabled, single-conductor, Type USE constructions rec- 
ognized for underground use may have a bare copper con- 
ductor cabled with the assembly. Type USE single, parallel, 
or cabled conductor assemblies recognized for underground 
use may have a bare copper concentric conductor applied. 
These constructions do not require an outer overall covering. 

FPN: See Section 230-41, Exception, item (b) for directly 
buried, uninsulated service-entrance conductors. 

(c) One Uninsulated Conductor. If Type SE or USE cable 
consists of two or more conductors, one shall be permitted 
to be uninsulated. 

338-2. Uses Permitted as Service-Entrance Conduc- 
tors. Service-entrance cable used as service-entrance con- 
ductors shall be installed as required by Article 230. 

Type USE used for service laterals shall be permitted to 
emerge above ground outside at terminations in meter bases 
or other enclosures where protected in accordance with Sec- 
tion 300-5(d). 

338-3. Uses Permitted as Branch Circuits or Feeders. 

(a) Grounded Conductor Insulated. Type SE service- 
entrance cables shall be permitted in interior wiring systems 
where all of the circuit conductors of the cable are of the 
rubber-covered or thermoplastic type. 



(c) Temperature Limitations. Type SE service-entrance 
cable used to supply appliances shall not be subject to con- 
ductor temperatures in excess of the temperature specified 
for the type of insulation involved. 

338-4. Installation Methods for Branch Circuits and 
Feeders. 

(a) Interior Installations. In addition to the provisions of 
this article, Type SE service-entrance cable used for interior 
wiring shall comply with the installation requirements of 
Parts A and B of Article 336 and shall comply with the 
applicable provisions of Article 300. 

FPN: See Section 310-10 for temperature limitation of 
conductors. 

(b) Exterior Installations. In addition to the provisions of 
this article, service-entrance cable used for feeders or branch 
circuits, where installed as exterior wiring, shall be installed 
as required by Article 225. The cable shall be supported in 
accordance with Section 336-18, unless used as messenger- 
supported wiring as allowed by Article 321. 

Type USE cable shall be installed outside in accordance 
with the provisions of Article 339. Where Type USE cable 
emerges above ground at terminations, it shall be protected 
in accordance with Section 300-5(d). 

Multiconductor service-entrance cable shall be permitted 
to be installed as messenger-supported wiring in accordance 
with Articles 225 and 321. 

338-5. Marking. Service-entrance cable shall be marked as 
required in Section 310-1 1. Cable with the neutral conductor 
smaller than the ungrounded conductors shall be so marked. 

338-6. Bends. Bends in cable shall be made, and other 
handlings shall be such, that the protective coverings of the 
cable will not be damaged, and the radius of the curve of 
the inner edge of any bend shall not be less than five times 
the diameter of the cable. 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-162 



ARTICLE 339 — UNDERGROUND FEEDER AND BRANCH-CIRCUIT CABLE: TYPE UF 



Article 339 — Underground Feeder and Branch- 
Circuit Cable: Type UF 

339-1. Description and Marking. 

(a) Description. Underground feeder and branch-circuit 
cable shall be a listed Type UF cable in sizes No. 14 copper 
or No. 12 aluminum or copper-clad aluminum through No. 
4/0. The conductors of Type UF shall be one of the moisture- 
resistant types listed in Table 310-13 that is suitable for 
branch-circuit wiring or one that is identified for such use. 
In addition to the insulated conductors, the cable shall be 
permitted to have an insulated or bare conductor for equip- 
ment grounding purposes only. The overall covering shall 
be flame retardant; moisture, fungus, and corrosion resistant; 
and suitable for direct burial in the earth. 

(b) Marking. The cable shall be marked in accordance 
with Section 310-11. 

339-2. Other Articles. In addition to the provisions of this 
article, installations of underground feeder and branch- 
circuit cable (Type UF) shall comply with other applicable 
provisions of this Code, especially Article 300 and Section 
310-13. 

339-3. Use. 

(a) Uses Permitted. 

(1) Type UF cable shall be permitted for use under- 
ground, including direct burial in the earth, as feeder or 
branch-circuit cable where provided with overcurrent pro- 
tection of the rated ampacity as required in Section 339-4. 

(2) Where single-conductor cables are installed, all ca- 
bles of the feeder circuit or branch circuit, including the 
neutral and equipment grounding conductor, if any, shall be 
run together in the same trench or raceway. 

(3) For underground requirements, see Section 300-5. 

(4) Type UF cable shall be permitted for interior wiring 
in wet, dry, or corrosive locations under the recognized 
wiring methods of this Code, and, where installed as 
nonmetallic- sheathed cable, the installation and conductor 
requirements shall comply with the provisions of Article 
336 and shall be of the multiconductor type. 

(5) For solar photovoltaic systems in accordance with 
Section 690-31. 

(6) Single-conductor cables shall be permitted as the non- 
heating leads for heating cables as provided in Section 424- 
43. 



Type UF cable supported by cable trays shall be of the 
multiconductor type. 

FPN: See Section 310-10 for temperature limitation of con- 
ductors. 

(b) Uses Not Permitted. Type UF cable shall not be used 
in the following: 

(1) As service-entrance cables 

(2) In commercial garages 

(3) In theaters 

(4) In motion picture studios 

(5) In storage battery rooms 

(6) In hoistways 

(7) In any hazardous (classified) location 

(8) Embedded in poured cement, concrete, or aggregate, 
except where embedded in plaster as nonheating leads 
as provided in Article 424 

(9) Where exposed to direct rays of the sun, unless identified 
as sunlight resistant 

(10) Where subject to physical damage 

339-4. Overcurrent Protection. Overcurrent protection 
shall be provided in accordance with the provisions of Sec- 
tion 240-3. 

339-5. Ampacity. The ampacity of Type UF cable shall be 
that of 60°C (140°F) conductors in accordance with Section 
310-15. 



• 



Article 340 
TypeTC 



Power and Control Tray Cable: 



340-1. Definition. Type TC power and control tray cable 
is a factory assembly of two or more insulated conductors, 
with or without associated bare or covered grounding con- 
ductors under a nonmetallic sheath, for installation in cable 
trays, in raceways, or where supported by a messenger wire. 

340-2. Other Articles. In addition to the provisions of this 
article, installations of Type TC tray cable shall comply with 
other applicable articles of this Code, especially Articles 
300 and 318. 

340-3. Construction. The insulated conductors of Type TC 
tray cable shall be in sizes No. 18 through 1000 kcmil copper 
and sizes No. 12 through 1000 kcmil aluminum or copper- 
clad aluminum. Insulated conductors of sizes No. 14 and 
larger copper and sizes No. 12 and larger aluminum or 
copper-clad aluminum shall be one of the types listed in 
Tables 310-13 or 310-62 that is suitable for branch circuit 
and feeder circuits or one that is identified for such use. The 
outer sheath shall be a flame-retardant, nonmetallic material. 



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1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 342 — NONMETALLIC EXTENSIONS 



70-163 



A metallic sheath shall not be permitted either under or over 
the rionmetallic sheath. 



340-5. Uses Not Permitted. Type TC tray cable shall not 
be used in the following: 



(a) Wet Locations. Where installed in wet locations, Type 
TC cable, shall also be resistant to moisture and corrosive 
agents. 

(b) Fire Alarm Systems. Where used for fire alarm sys- 
tems, conductors shall also be in accordance with Section 
760-27. 

(c) Thermocouple Circuits. Conductors in Type TC ca- 
bles used for thermocouple circuits in accordance with Arti- 
cle 725 shall also be permitted to be any of the materials 
used for thermocouple extension wire. 

There shall be no voltage marking on a Type TC cable 
employing thermocouple extension wire. 

(d) Class 1 Circuit Conductors. Insulated conductors of 
sizes No. 18 and No. 16 copper shall also be in accordance 
with Section 725-27. 

340-4. Use Permitted. Type TC tray cable shall be per- 
mitted to be used in the following. 

■*■' '■■ < 

(1) For power, lighting, control, and signal circuits. 

(2) In cable trays, or in raceways, or where supported in 
outdoor locations by a messenger wire, 

(3) In cable trays in hazardous (classified) locations as per- 
mitted in Articles 318, 501, 502, 504, and 505 in indus- 
trial establishments where the conditions of maintenance 
and supervision ensure that only qualified persons will 
service the installation. 

(4) For Class 1 circuits as permitted in Article 725. 

(5) For nonpower-limited fire alarm circuits if conductors 
comply with the requirements of.,Section 760-27. 

(6) In industrial establishments where the conditions of 
maintenance and supervision ensure that only qualified 
persons will service the installation, and where the cable 
is not subject to physical damage, Type TC, tray cable 
that complies with the crush and impact requirements 
of Type MC cable and is identified for such use shall 
be 1 permitted, as open wiringin lengths not to exceed a 
total of 50 ft (15.24 m) between a cable tray and .the 
utilization equipment or device. 

The cable shall be supported and secured at intervals 
not exceeding 6 ft (1.83 m). 

Equipment grounding for the utilization equipment 
shall be provided by an equipment grounding conductor 
within the cable. 

FPN: See Section 310-10 for temperature limitation of con- 
ductors. 



(1) Installed where it will be exposed to physical damage 

(2) Installed as open cable on brackets or cleats 

(3) Used where exposed to direct rays of the sun, unless 
identified as sunlight resistant 

(4) Direct buried, unless identified for such use 



340-6. Marking. The cable shall be marked in accordance 
with Section 310-11. 

340-7. Ampacity. The ampacities of the conductors of 
Type TC tray cable shall be determined from Section 
402-5 for conductors smaller than No. 14 and from Section 
318-11. 

340-8. Bends. Bends in Type TC cable shall be made so 
as not to damage the cable. 

Article 342 — Nonmetallic Extensions 

342-1. Definition. Nonmetallic extensions are an assembly 
of two insulated conductors within a nonmetallic jacket or an 
extruded thermoplastic covering. The classification includes 
both surface extensions, intended for mounting directly on 
the surface of walls or ceilings, and aerial cable containing 
a supporting messenger cable as an integral part of the cable 
assembly. 

342-2. Other Articles. In addition to the provisions of this 
article, nonmetallic extensions shall be installed in accor- 
dance with the applicable provisions of this Code. 

342-3.. Uses Permitted. Nonmetallic extensions shall be 
permitted only where all of the following conditions- are 
met: 

(a) From an Existing Outlet. The extension is from, an 
existing outlet on a 15- or 20-ampere branch circuit in con- 
formity with the requirements of Article 210. 

(b) Exposed and in a Dry Location. The extension is run 
exposed and in a dry location. 

(c) Nonmetallic Surface Extensions. For nonmetallic sur- 
face extensions, the building is occupied for residential or 
office purposes and does not exceed the height limitations 
specified in Section 336-5(a)(l). 

(cl) [Alternate to (c)]. For aerial cable, the building is 
occupied for industrial purposes, and the nature of the occu- 



NATIONAL ELECTRICAL CODE 



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70-164 



ARTICLE 343 — NONMETALLIC UNDERGROUND CONDUIT WITH CONDUCTORS 



pancy requires a highly flexible means for connecting equip- 
ment. 

FPN: See Section 310-10 for temperature limitation of con- 
ductors. 



342-4. Uses Not Permitted. 

not be used as follows. 



Nonmetallic extensions shall 



(a) Aerial Cable. As aerial cable to substitute for one of 
the general wiring methods specified by this Code. 

(b) Unfinished Areas. In unfinished basements, attics, or 
roof spaces. 

(c) Voltage Between Conductors. Where the voltage be- 
tween conductors exceeds 150 volts for nonmetallic surface 
extension and 300 volts for aerial cable. 

(d) Corrosive Vapors. Where subject to corrosive vapors. 

(e) Through a Floor or Partition. Where run through a 
floor or partition, or outside the room in which it originates. 

342-5. Splices and Taps. Extensions shall consist of a con- 
tinuous unbroken length of the assembly, without splices, 
and without exposed conductors between fittings. Taps shall 
be permitted where approved fittings completely covering 
the tap connections are used. Aerial cable and its tap connec- 
tors shall be provided with an approved means for polariza- 
tion. Receptacle-type tap connectors shall be of the locking 
type. 

342-6. Fittings. Each run shall terminate in a fitting that 
covers the end of the assembly. All fittings and devices shall 
be of a type identified for the Use. 

342-7. Installation. Nonmetallic extensions shall be in- 
stalled as specified in (a) and (b). 

(a) Nonmetallic Surface Extensions. i 

(1) One or more extensions shall be permitted to be run 
in any direction from an existing outlet, but not on the floor 
or within 2 in. (50.8 mm) from the floor. 

(2) Nonmetallic surface extensions shall be secured in 
place by approved means at intervals not exceeding 8 in. 
(203 mm), with an allowance for 12 in. (305 mm) to the 
first fastening where the connection to the supplying outlet 
is by means of an attachment plug. There shall be at least 
one fastening between each two adjacent outlets supplied. 
An extension shall be attached to only woodwork or plaster 
finish, and shall not be in contact with any metal work or 
other conductive material other than with metal plates on 
receptacles. 



(3) A bend that reduces the normal spacing between the 
conductors shall be covered with a cap to protect the assem- 
bly from physical damage. 

(b) Aerial Cable. 

(1) Aerial cable shall be supported by its messenger cable 
and securely attached at each end with clamps and turnbuck- 
les. Intermediate supports shall be provided at not more than 
20-ft (6.1-m) intervals. Cable tension shall be adjusted to 
eliminate excessive sag. The cable shall have a clearance of 
not less than 2 in. (50.8 mm) from steel structural members 
or other conductive material. 

(2) Aerial cable shall have a clearance of not less than 
10 ft (3.05 m) above floor areas accessible to pedestrian 
traffic, and not less than 14 ft (4.27 m) above floor areas 
accessible to vehicular traffic. 

(3) Cable suspended over work benches, not accessible 
to pedestrian traffic, shall have a clearance of not less than 
8 ft (2.44 m) above the floor. 

(4) Aerial cables shall be permitted as a means to support 
lighting fixtures where the total load on the supporting mes- 
senger cable does not exceed that for which the assembly 
is intended. 

(5) The supporting messenger cable, where installed in 
conformity with the applicable provisions of Article 250 and 
if properly identified as an equipment grounding conductor, 
shall be permitted to ground equipment: The messenger 
cable shall not be used as a branch-circuit conductor. 

342-8. Marking. Nonmetallic extensions shall be marked 
in accordance with Section 110-21. 

Article 343 — Nonmetallic Underground Conduit 
with Conductors 

A. General 

343-1. Description. Nonmetallic underground conduit with 
conductors is a factory assembly of conductors or cables 
inside a nonmetallic, smooth wall conduit with a circular 
cross section. 

The nonmetallic conduit shall be composed of a material 
that is resistant to moisture and corrosive agents. It shall 
also be capable of being supplied on reels without damage 
or distortion and shall be of sufficient strength to withstand 
abuse, such as impact or crushing, in handling and during 
installation without damage to conduit or conductors. 

343-2. Other Articles. Installations for nonmetallic under- 
ground conduit with conductors shall comply with the pro- 
visions of the applicable sections of Article 300. Where 
equipment grounding is required by Article 250, an assembly 



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ARTICLE 343 — NONMETALLIC UNDERGROUND CONDUIT WITH CONDUCTORS 



70-165 



containing a separate equipment grounding conductor shall 
be used. 

343-3. Uses Permitted. The use of listed nonmetallic un- 
derground conduit with conductors and fittings shall be per- 
mitted in the following. 



343-7. Joints. All joints between conduit, fittings, and 
boxes shall be made by an approved method. 

343-8. Conductor Terminations. All terminations be- 
tween the conductors or cables and equipment shall be made 
by an approved method for that type of conductor or cable. 



(1) For direct burial underground installation. For mini- 
mum cover requirements, see Tables 300-5 and 300-50 
under rigid nonmetallic conduit. 

(2) Encased or embedded in concrete. 

(3) In cinder fill. 

(4) In underground locations subject to severe corrosive 
influences as covered in Section 300-6 and where subject 
to chemicals for which the assembly is specifically ap- 
proved. 

343-4. Uses Not Permitted. Nonmetallic underground 
conduit with conductors shall not be used in the following: 

(1) In exposed locations 

(2) Inside buildings 

Exception: The conductor or the cable portion of the as- 
sembly, where suitable, shall be permitted to extend within 
the building for termination purposes in accordance with 
Section 300-3. 

(3) In hazardous (classified) locations except as permitted 
by Sections 503-3(a), 504-20, 514-8, and 515-5, and in 
Class I, Division 2 locations as permitted in Section 
501 -4(b), Exception 

B. Installation 
343-5. Size. 

(a) Minimum. Nonmetallic underground conduit with con- 
ductors smaller than !/2-in. electrical trade size shall not be 
used. 

(b) Maximum. Nonmetallic underground conduit with 
conductors larger than 4-in. electrical trade size shall not be 
used. 

FPN: Metric trade numerical designations for nonmetallic 
underground conduit with conductors are Vi = 16, 3 A = 21, 

1 = 27, l'/ 4 = 35, VA = 41, 2 = 53, 2Vi = 63, 3 = 78, 
3'/ 2 = 91, and 4 = 103. 

343-6. Trimming. For termination, the conduit shall be 
trimmed away from the conductors or cables using an ap- 
proved method that will not damage the conductor or cable 
insulation or jacket. All ends shall be trimmed inside and 
out to remove rough edges. 



343-9. Bushings. Where the nonmetallic underground con- 
duit with conductors enters a box, fitting, or other enclosure, 
a bushing or adapter shall be provided to protect the conduc- 
tor or cable from abrasion unless the design of the box, 
fitting, or enclosure provides equivalent protection. 

FPN: See Section 300-4(f) for the protection of conductors 
size No. 4 or larger. 

343-10. Bends — How Made. Bends of nonmetallic un- 
derground conduit with conductors shall be manually made 
so that the conduit will not be damaged and the internal 
diameter of the conduit will not be effectively reduced. The 
radius of the curve of the centerline of such bends shall not 
be' less than shown in Table 343-10. 

Table 343-10. Radius of Conduit Bends 



Trade Size 




Minimum 


Bending Radius 


(in.) 






(in.) 


'/2 






10 


3 /4 






12 


1 






14 


VA 






18 


Vh 






20 


2 






26 


2Vi 






36 


3 






48 


4 






60 


Note: For SI units, in. 


= 25.4 


mm (radius). 





343-11. Bends — Number in One Run. There shall not 
be more than the equivalent of four quarter bends (360 
degrees total) between termination points. 

343-12. Splices and Taps. Splices and taps shall be made 
in junction boxes or other enclosures. See Article 370 for 
rules on the installation and use of boxes and conduit bodies. 



C. Construction 

343-13. General. Nonmetallic underground conduit with 
conductors is an assembly that is provided in continuous 
lengths shipped in a coil, reel, or carton. 

343-14. Conductors and Cables. Conductors and cables 
used in nonmetallic underground conduit with conductors 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-166 



ARTICLE 345 — INTERMEDIATE METAL CONDUIT 



shall be listed, shall be suitable for use in wet locations, and 
shall be as follows. 

(a) 600 Volts or Less. Alternating-current and direct-cur- 
rent circuits shall be permitted. All conductors shall have 
an insulation rating equal to at least the maximum nominal 
circuit voltage of any conductor or cable within the conduit. 

(b) Over 600 Volts. Conductors or cables rated over 600 
volts shall not occupy the same conduit with conductors or 
cables of circuits rated 600 volts or less. 

343-15. Conductor Fill. The maximum number of con- 
ductors or cables in nonmetallic underground conduit with 
conductors shall not exceed that permitted by the percentage 
fill in Table 1, Chapter 9. 

343-16. Marking. Nonmetallic underground conduit with 
conductors shall be clearly and durably marked at least every 
10 ft (3.05 m) as required by Section 110-21. The type of 
conduit material shall also be included in the marking. 

Identification of conductors or cables used in the assem- 
bly shall be provided on a tag attached to each end of the 
assembly or to the side of a reel. Enclosed conductors or 
cables shall be marked in accordance with Section 310-11. 

Article 345 — Intermediate Metal Conduit 

A. General 

345-1. Definition. Intermediate metal conduit is a listed 
steel raceway of circular cross section with integral or asso- 
ciated couplings, approved for the installation of electrical 
conductors and used with listed fittings to provide electrical 
continuity. 

345-2. Other Articles. Installations for intermediate metal 
conduit shall comply with the provisions of the applicable 
sections of Article 300. 

345-3. Uses Permitted. 

(a) All Atmospheric Conditions and Occupancies. Use 

of intermediate metal conduit shall be permitted under all 
atmospheric conditions and occupancies. Where practicable, 
dissimilar metals in contact anywhere in the system shall 
be avoided to eliminate the possibility of galvanic action. 
Intermediate metal conduit shall be permitted as an equip- 
ment grounding conductor. 

Exception: Aluminum fittings and enclosures shall be per- 
mitted to be used with steel intermediate metal conduit. 

(b) Corrosion Protection. Intermediate metal conduit, el- 
bows, couplings, and fittings shall be permitted to be in- 
stalled in concrete, in direct contact with the earth, or in 



areas subject to severe corrosive influences where protected 
by corrosion protection and judged suitable for the condition. 

FPN: See Section 300-6 for protection against corrosion. 

(c) Cinder. Fill. Intermediate metal conduit shall be per- 
mitted to be installed in or under cinder fill where subject 
to permanent moisture where protected on all sides by a 
layer of noncinder concrete not less than 2 in. (50.8 mm) 
thick; where the conduit is not less than 18 in. (457 mm) 
under the fill; or where protected by corrosion protection 
and judged suitable for the condition. 

FPN: See Section 300-6 for protection against corrosion. 



B. Installation 

345-5. Wet Locations. All supports, bolts, straps, screws, 
etc., shall be of corrosion-resistant materials or protected 
against corrosion by corrosion-resistant materials. 

FPN: See Section 300-6 for protection against corrosion. 

345-6. Size. 

(a) Minimum. Conduit smaller than Vi-in. electrical trade 
size shall not be used. 

(b) Maximum. Conduit larger than 4-in. electrical trade 
size shall not be used. 

FPN: Metric trade numerical designations for intermediate 
metal conduit are the same as those found in Extra-heavy 
Duty Rigid Steel Conduits for Electrical Installations, IEC 
981-1989; namely, Vi = 16, 3 / 4 = 21, 1 = 27, VA = 35, VA 
= 41, 2 = 53, 2'/ 2 = 63, 3 = 78, VA = 91, and 4 = 103. 

345-7. Number of Conductors in Conduit. The number 
of conductors in a single conduit shall not exceed that 
permitted by the percentage fill specified in Table 1, Chap- 
ter 9, using the conduit dimensions of Table 4, Chapter 9. 

345-8. Reaming and Threading. All cut ends of conduits 
shall be reamed or otherwise finished to remove rough edges. 
Where conduit is threaded in the field, a standard cutting 
die with a 3 /4-in. taper per foot (1 in 16) shall be used. 

FPN: See Standards for Pipe Threads, General Purpose 
(Inch), ANSI/ASME B. 1.20.1-1983. 

345-9. Couplings arid Connectors. 

(a) Threadless. Threadless couplings and connectors used 
with conduit shall be made tight. Where buried in masonry 
or concrete, they shall be the concretetight type. Where 
installed in wet locations, they shall be the raintight type. 

(b) Running Threads. Running threads shall not be used 
on conduit for connection at couplings. 



• 



• 



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ARTICLE 346 — RIGID METAL CONDUIT 



70-167 



345-10. Bends — How Made. Bends of intermediate metal 
conduit shall be made so that the conduit will not be damaged 
and so that the internal diameter of the conduit will not be 
effectively reduced. The radius of the curve of the inner 
edge of any field bend shall not be less than indicated in 
Table 346-10. 

Exception: For field bends for conductors without lead 
sheath and made with a single operation (one shot) bending 
machine designed for the purpose, the minimum radius shall 
not be less than that indicated in Table 346-10, Exception. 

345-11. Bends — Number in One Run. There shall not 
be more than the equivalent of four quarter bends (360 
degrees total) between pull points, e.g., conduit bodies and 
.boxes. 

345-12. Securing and Supporting. Intermediate metal 
conduit shall be installed as a complete system as provided 
in, Article 300 and shall be securely fastened in place and 
supported in accordance with (a) and (b). 

(a) Securely Fastened. Each intermediate metal conduit 
shall be securely fastened within 3 ft (914 mm) of each 
outlet box, junction box, device box, cabinet, conduit body, 
or other conduit termination. Fastening shall be permitted 
to be increased to a distance of 5 ft (1.52 m) where structural 
members do riot readily permit fastening within 3 ft (914 
mm). Where approved, conduit shall not be required to be 
securely fastened within 3 ft (914 mm) of the service head 
for above-the-roof termination of a mast. 



(b) Supports. Intermediate metal conduit shall be sup- 
ported in accordance with one of the following. 

(1) Conduit shall be supported at intervals not exceeding 
10 ft (3.05 m). 

(2) The distance between supports for straight runs of 
conduit shall be permitted in accordance with Table 346- 
12, provided the conduit is made up with threaded couplings, 
and such supports prevent transmission of stresses to termi- 
nation where conduit is deflected between supports. 

(3) Exposed vertical risers from industrial machinery 
shall be permitted to be supported at intervals not exceeding 
20 ft (6. 1 m), provided the conduit is made up with threaded 
couplings, is firmly supported at the top and bottom of the 
riser, and no other means of intermediate support is readily 
available. 

(4) Horizontal runs of intermediate metal conduit sup- 
ported by openings through framing members at intervals 



not exceeding 10 ft (3.05 m) and securely fastened within 
3 ft (914 mm) of termination points shall be permitted. 

345-13. Boxes and Fittings. See Article 370. 

345-14. Splices and Taps. Splices and taps shall be made 
in accordance with Section 300-15. See Article 370 for rules 
on the installation and use of boxes and conduit bodies. 

345-15. Bushings.' Where a conduit enters a box, fitting, 
or other enclosure, a bushing shall be provided to protect 
the wire from abrasion unless the design of the box, fitting, 
or enclosure is such as to afford equivalent protection. 

FPN: See Section 300-4(f) for the protection of conductors 
sizes No. 4 and larger at bushings. 

C. Construction Specifications 

345-16. General. Intermediate metal conduit shall comply 
with (a) through (c). 

(a) Standard Lengths. The standard length of intermediate 
metal conduit shall be 10 ft (3.05 m), including an attached 
coupling, and each end shall be threaded. Longer or shorter 
lengths with or without coupling and threaded or unthreaded 
shall be permitted. 

(b) Corrosion-Resistant Material. Nonferrous conduit of 
corrosion-resistant material shall have suitable markings. 

(c) Marking. Each length shall be clearly and durably 
marked at least every 5 ft (1.52 m) with the letters IMC. 
Each length shall be marked as required in the first sentence 
of Section 110-21. 

Article 346 — Rigid Metal Conduit 

A. General 

346-1. Definition. Rigid metal conduit is a listed metal 
raceway of circular cross section with integral or associated 
couplings, approved for the installation of electrical conduc- 
tors and used with listed fittings to provide electrical conti- 
nuity. 

346-2. Other Articles. Installations for rigid metal conduit 
shall comply with the provisions of the applicable sections 
of Article 300. 

346-3. Uses Permitted. 

(a) All Atmospheric Conditions and Occupancies. Use 

of rigid metal conduit shall be permitted under all atmo- 
spheric conditions and occupancies. Where practicable, dis- 
similar metals in contact anywhere in the system shall be 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-168 



ARTICLE 346 — RIGID METAL CONDUIT 



avoided to eliminate the possibility of galvanic action. Rigid 
metal conduit shall be permitted as an equipment grounding 
conductor. Ferrous raceways and fittings protected from cor- 
rosion solely by enamel shall be permitted only indoors and 
in occupancies not subject to severe corrosive influences. 

Aluminum fittings and enclosures shall be permitted to 
be used with steel rigid metal conduit, and steel fittings and 
enclosures shall be permitted to be used with aluminum rigid 
metal conduit. 



mitted by the percentage fill specified in Table 1, Chap- 
ter 9, using the conduit dimensions of Table 4, Chapter 9. 

346-8. Reaming and Threading. All cut ends of conduits 
shall be reamed or otherwise finished to remove rough edges. 
Where conduit is threaded in the field, a standard cutting 
die with a 3 /4-in. taper per foot (1 in 16) shall be used. 

FPN: See Standards for Pipe Threads, General Purpose 
(Inch), ANSI/ASME B. 1.20.1-1983. 



• 



• 



(b) Corrosion Protection. Rigid metal conduit, elbows, 
couplings, and fittings shall be permitted to be installed in 
concrete, in direct contact with the earth, or in areas subject 
to severe corrosive influences where protected by corrosion 
protection and judged suitable for the condition. 

FPN: See Section 300-6 for protection against corrosion. 

(c) Cinder Fill. Rigid metal conduit shall be permitted to 
be installed in or under cinder fill where subject to permanent 
moisture where protected on all sides by a layer of noncinder 
concrete not less than 2 in. (50.8 mm) thick; where the 
conduit is not less than 18 in. (457 mm) under the fill; or 
where protected by corrosion protection and judged suitable 
for the condition. 

FPN: See Section 300-6 for protection against corrosion. 



B. Installation 

346-5. Wet Locations. All supports, bolts, straps, screws, 
etc., shall be of corrosion-resistant materials or protected 
against corrosion by corrosion-resistant materials. 

FPN: See Section 300-6 for protection against corrosion. 

346-6. Size. 

(a) Minimum. Rigid metal conduit smaller than V^-in. elec- 
trical trade size shall not be used. 

Exception: For enclosing the leads of motors as permitted 
in Section 430-145(b). 

(b) Maximum. Rigid metal conduit larger than 6-in. elec- 
trical trade size shall not be used. 

FPN: Metric trade numerical designations for rigid metal 
conduit are the same as those found in Extra-heavy Duty 
Rigid Steel Conduits for Electrical Installations, IEC 981- 
1989; namely, Vi = 16, Va = 21, 1 = 27, VA = 35, VA = 
41, 2 = 53, 2 l A = 63, 3 = 78, 3'/ 2 = 91, 4 = 103, 5 = 
129, and 6 = 155. 

346-7. Number of Conductors in Conduit. The number 
of conductors in a single conduit shall not exceed that per- 



346-9. Couplings and Connectors. 

(a) Threadless. Threadless couplings and connectors used 
with conduit shall be made tight. Where buried in masonry 
or concrete, they shall be the concretetight type. Where 
installed in wet locations, they shall be the raintight type. 

(b) Running Threads. Running threads shall not be used 
on conduit for connection at couplings. 

346-10. Bends - — How Made. Bends of rigid metal con- 
duit shall be made so that the conduit will not be damaged 
and that the internal diameter of the conduit will not be 
effectively reduced. The radius of the curve of the inner 
edge of any field bend shall not be less than indicated in 
Table 346-10. 

Table 346-10. Radius of Conduit Bends 



• 







Conductors Without 


Size of Conduit 


Lead Sheath 


(in.) 






(in.) 


Vi 






4 


3 /4 






5 


1 






6 


VA 






8 


V/2 






10 


2 






12 


2Vi 






15 


3 






18 


3'/2 






21 


4 






24 


5 






30 


6 






36 


Note: For SI units, 1 in. = 


25.4 


mm (radius) 





Exception: For field bends for conductors without lead 
sheath and made with a single operation (one shot) bending 
machine designed for the purpose, the minimum radius shall 
not be less than that indicated in Table 346-10, Exception. 

346-11. Bends — Number in One Run. There shall not 
be more than the equivalent of four quarter bends (360 
degrees total) between pull points, e.g., conduit bodies and 
boxes. 



• 



1999 Edition 



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ARTICLE 347 — RIGID NONMETALLIC CONDUIT 



70-169 



Table 346-10. Exception, Radius of Conduit Bends 



Table 346-12(b)(2). Supports for Rigid Metal Conduit 



Size of Conduit 
(in.) 



Radius to 
Center of Conduit 

(in.) 



>/2 


4 


3 A 


4'h 


I 


5 3 A 


1>A 


7>A 


l'A 


8'A 


2 


9'h 


2'A 


10'A 


3 


13 


3'/2 


15 


4 , 


16 


5 


24 


6 


30 



Note: For SI units, 1 in. = 25.4 mm (radius). 

346-12. Securing and Supporting. Rigid metal conduit 
shall be installed as a complete system as provided in Article 
300 and shall be securely fastened in place and supported 
in accordance with (a) and (b). 

(a) Securely Fastened. Each rigid metal conduit shall be 
securely fastened within 3 ft (914 mm) of each outlet box, 
junction box, device box, cabinet, conduit body, or other 
conduit termination. Fastening shall be permitted to be in- 
creased to a distance of 5 ft (1.52 m) where structural mem- 
bers do not readily permit fastening within 3 ft (914 mm). 
Where approved, conduit shall not be required to be securely 
fastened within 3 ft (914 mm) of the service head for above- 
the-roof termination of a mast. 



(b) Supports. Rigid metal conduit shall be supported in 
accordance with one of the following. 

(1) Conduit shall be supported at intervals not exceeding 
10 ft (3.05 m). 

(2) The distance between supports for straight runs of 
conduit shall be permitted in accordance with Table 346- 
12(b)(2), provided the conduit is made up with threaded 
couplings, and such supports prevent transmission of stresses 
to termination where conduit is deflected between supports. 

(3) Exposed vertical risers from stationary equipment or 
fixtures shall be permitted to be supported at intervals not 
exceeding 20 ft (6.1 m), provided the conduit is made up 
with threaded couplings, is firmly supported at the top and 
bottom of the riser, and no other means of intermediate 
support is readily available. 

(4) Horizontal runs of rigid metal conduit supported by 
openings through framing members at intervals not exceed- 
ing 10 ft (3.05 m) and securely fastened within 3 ft (914 
mm) of termination points shall be permitted. 





Maximum Distance 




Between Rigid 


Conduit Size 


Metal Conduit 


(in.) 


Supports (ft) 



'/2- 3 /4 


10 


1 


12 


VA-VA 


14 


2~2Vi 


16 


3 and larger 


20 



Note: For SI units, 1 ft = 0.3048 m (supports). 



346-13. Boxes and Fittings. See Article 370. 

346-14. Splices and Taps. Splices and taps shall be made 
in accordance with Section 300-15. See Article 370 for rules 
on the installation and use of boxes and conduit bodies. 

346-15. Bushings. Where a conduit enters a box, fitting, 
or other enclosure, a bushing shall be provided to protect 
the wire from abrasion unless the design of the box, fitting, 
or enclosure is such as to afford equivalent protection. 

FPN: See Section 300-4(f) for the protection of conductors 
sizes No. 4 and larger at bushings. 

C. Construction Specifications 

346-16. General. Rigid metal conduit shall comply with 
(a) through (c). 

(a) Standard Lengths. The standard length of rigid metal 
conduit shall be 10 ft (3.05 m), including an attached 
coupling, and each end shall be threaded. Longer or shorter 
lengths with or without coupling and threaded or unthreaded 
shall be permitted. 

(b) Corrosion-Resistant Material. Nonferrous conduit of 
corrosion-resistant material shall have suitable markings. 

(c) Marking. Each length shall be clearly and durably iden- 
tified in every 10 ft (3.05 m) as required in the first sentence 
of Section 110-21. 

Article 347 — Rigid Nonmetallic Conduit 

347-1. Description. This article shall apply to a type of 
conduit and fittings of suitable nonmetallic material that is 
resistant to moisture arid chemical atmospheres. For use 
aboveground, it shall also be flame retardant, resistant to 
impact and crushing, resistant to distortion from heat under 
conditions likely to be encountered in service, and resistant 
to low temperature and sunlight effects. For use under- 
ground, the material shall be acceptably resistant to moisture 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-170 



ARTICLE 347 — RIGID NONMETALLIC CONDUIT 



and corrosive agents and shall be of sufficient strength to 
withstand abuse, such as by impact and crushing, in handling 
and during installation. Conduits listed for the purpose shall 
be permitted to be installed underground in continuous 
lengths from a reel. Where intended for direct burial, without 
encasement in concrete, the material shall also be capable 
of withstanding continued loading that is likely to be encoun- 
tered after installation. 

347-2. Uses Permitted. The use of listed rigid nonmetallic 
conduit shall be permitted under the following conditions. 

FPN: Extreme cold may cause some nonmetallic conduits 
to become brittle and therefore more susceptible to damage 
from physical contact. 

(a) Concealed. In walls, floors, and ceilings. 

(b) Corrosive Influences. In locations subject to severe 
corrosive influences as covered in Section 300-6 and where 
subject to chemicals for which the materials are specifically 
approved. 

(c) Cinders. In cinder fill. 

(d) Wet Locations. In portions of dairies, laundries, can- 
neries, or other wet locations and in locations where walls 
are frequently washed, the entire conduit system including 
boxes and fittings used therewith shall be installed and 
equipped so as to prevent water from entering the conduit. 
All supports, bolts, straps, screws, etc., shall be of corrosion- 
resistant materials or be protected against corrosion by ap- 
proved corrosion-resistant materials. 

(e) Dry and Damp Locations. In dry and damp locations 
not prohibited by Section 347-3. 

(f) Exposed. For exposed work where not subject to phys- 
ical damage if identified for such use. 

(g) Underground Installations. For underground instal- 
lations, see Sections 300-5 and 300-50. 

(h) Support of Conduit Bodies. Rigid nonmetallic conduit 
shall be permitted to support nonmetallic conduit bodies not 
larger than the largest trade size of an entering raceway. The 
conduit bodies shall not contain devices or support fixtures 
or other equipment. 

347-3. Uses Not Permitted. Rigid nonmetallic conduit 
shall not be used in the following locations. 

(a) Hazardous (Classified) Locations. 

(1) In hazardous (classified) locations, except as covered in 
Sections 503-3(a),- 504-20, 514-8, and 515-5 



(2) In Class I, Division 2 locations, except as permitted in 
Section 501 -4(b), Exception 

(b) Support of Fixtures. For the support of fixtures or 
other equipment not described in Section 347-2(h). 

(c) Physical Damage. Where subject to physical damage 
unless identified for such use. 

(d) Ambient Temperatures. Where subject to ambient 
temperatures in excess of 50°C (122°F) unless listed other- 
wise. 

(e) Insulation Temperature Limitations. For conductors 
whose insulation temperature limitations would exceed those 
for which the conduit is listed. 

(f) Theaters and Similar Locations. In theaters and sim- 
ilar locations, except as provided in Articles 518 and 520. 

347-4. Other Articles. Installation of rigid nonmetallic 
conduit shall comply with the applicable provisions of Arti- 
cle 300. Where equipment grounding is required by Article 
250, a separate equipment grounding conductor shall be 
installed in the conduit. 

Exception No. 1: As permitted in Section 250-1 34(b), Ex- 
ception No. 2, for dc circuits and Section 250-1 34(b), Excep- 
tion No. 1, for separately run equipment grounding 
conductors. 

Exception No. 2: Where the grounded conductor is used to 
ground equipment as permitted in Section 250-142. 

A. Installations 

347-5. Trimming. All cut ends shall be trimmed inside and 
outside to remove rough edges. 

347-6. Joints. All joints between lengths of conduit, and 
between conduit and couplings, fittings, and boxes, shall be 
made by an approved method. 

347-8. Securing and Supporting. Rigid nonmetallic con- 
duit shall be installed as a complete system as provided in 
Section 300-18 and shall be fastened so that movement from 
thermal expansion or contraction will be permitted. Rigid 
nonmetallic conduit shall be securely fastened and supported 
in accordance with (a) and (b). 

(a) Securely Fastened. Each rigid nonmetallic conduit 
shall be securely fastened within 3 ft (914 mm) of each 
outlet box, junction box, device box, conduit body, or other 
conduit termination. Conduit listed for securing at other than 
3 ft (914 mm) shall be permitted to be installed in accordance 
with the listing. 



• 



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1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 347 — RIGID NONMETALLIC CONDUIT 



70-171 



(b) Supports. Rigid nonmetallic conduit shall be supported 
as required in Table 347-8. Conduit listed for support at 
spacings other than as shown in Table 347-8 shall be per- 
mitted to be installed in accordance with the listing. Hori- 
zontal runs of rigid nonmetallic conduit supported by open- 
ings through framing members at intervals not exceeding 
those in Table 347-8 and securely fastened within 3 ft (914 
mm) of termination points shall be permitted. 

Table 347-8. Support of Rigid Nonmetallic Conduit 



Conduit Size 
(in.) 



Maximum Spacing 
Between Supports 

(ft) 



'/2-1 


3 


VA-2 


5 


2V4-3 


6 


3'/ 2 -5 


7 


6 


8 



Note: For SI units, 1 ft = 0.3048 m (supports). 



347-9. Expansion Fittings. Expansion fittings for rigid 
nonmetallic conduit shall be provided to compensate for 
thermal expansion and contraction where the length change, 
in accordance with Tables 347-9(A) and (B), is expected to 
be l A in. (6.36 mm) or greater in a straight run between 
securely mounted items such as boxes, cabinets, elbows, or 
other conduit terminations. 



347-10. Size. 

(a) Minimum. Rigid nonmetallic conduit smaller than 
V2-in. electrical trade size shall not be used. 

(b) Maximum. Rigid nonmetallic conduit larger than 6-in. 
electrical trade size shall not be used. 

FPN: Metric trade numerical designations for rigid nonme- 
tallic conduit are l A = 16, % = 21, 1 = 27, VA = 35, V/i 

= 41, 2 = 53, 2'/ 2 = 63, 3 = 78, 3Vi = 91, 4 = 103, 5 = 
129, and 6 = 155. 

347-11. Number of Conductors. The number of conduc- 
tors permitted in a single conduit shall not exceed the per- 
centage fill specified in Table 1, Chapter 9. 

347-12. Bushings. Where a conduit enters a box, fitting, 
or other enclosure, a bushing or adapter shall be provided 
to protect the wire from abrasion unless the box, fitting, or 
enclosure design provides equivalent protection. 

FPN: See Section 300-4(f) for the protection of conductors 
No. 4 and larger at bushings. 

347-13. Bends — How Made. Bends of rigid nonmetallic 
conduit shall be made so that the conduit will not be damaged 
and that the internal diameter of the conduit will not be 
effectively reduced. Field bends shall be made only with 
bending equipment identified for the purpose, and the radius 



Table 347-9(A). Expansion Characteristics of PVC Rigid Nonmetallic Conduit Coefficient of 
Thermal Expansion = 3.38 x 10" s in./in./°F 



• 



Temperature 


Length Change of 


Temperature 


Length Change of 


Change 


PVC Conduit 


Change 


PVC Conduit 


(°F) 


(in./100 ft) 


(°F) 


(in./100 ft) 


5 


0.2 


105 


4.2 


10 


0.4 


110 


4.5 


15 


0.6 


115 


4.7 


20 


0.8 


120 


4.9 


25 


1.0 


125 


5.1 


30 


1.2 


130 


5.3 


35 


1.4 


135 


5.5 


40 


1.6 


140 


5.7 


45 


1.8 


145 


5.9 


50 


2.0 


150 


6.1 


55 


2.2 


155 


6.3 


60 


2.4 


160 


6.5 


65 


2.6 


165 


6.7 


70 


2.8 


170 


6.9 


75 


3.0 


175 


7.1 


80 


3.2 


180 


7.3 


85 


3.4 


185 


7.5 


90 


3.6 


190 


'7.7 


95 


3.8 


195 


7.9 


100 


4.1 


200 


8.1 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-172 



ARTICLE 348 — ELECTRICAL METALLIC TUBING 



Table 347-9(B). Expansion Characteristics of Fiberglass Reinforced Conduit (Rigid Nonmetallic 
Conduit) Coefficient of Thermal Expansion = 1.5 x 10 -5 in./in./°F 



Temperature 


Length Change of 


Temperature 


Length Change of 


Change 


PVC Conduit 


Change 


PVC Conduit 


(°F) 


(in./100 ft) 


(°F) 


(in./100 ft) 


5 


0.1 


105 


1.9 


10 


0.2 


110 


2.0 


15 


0.3 


115 


2.1 


20 


0.4 


120 


2.2 


25 


0.5 


125 


2.3 


30 


0.5 


130 


2.3 


35 


0.6 


135 


2.4 


40 


0.7 


140 


2.5 


45 


0.8 


145 


2.6 


50 


0.9 . 


150 


2.7 


55 


1.0 


155 


2.8 


60 


1.1 


160 


2.9 


65 


1.2 


165 


3.0 


70 


1.3 


170 


3.1 


75 


1.4 


175 


3.2 


80 


1.4 


180 • 


3.2 


85 


1.5 


185, 


3.3 


90 


1.6 


190 


3.4 


95 


1.7 


195 


3.5 


100 


1.8 


200 


3.6 



• 



of the curve of the inner edge of such bends shall not be 
less than shown in Table 346-10. 

347-14. Bends — Number in One Run. There shall not 
be more than the equivalent of four quarter bends (360 
degrees total) between pull points, e.g., conduit bodies and 
boxes. 

347-15. Boxes and Fittings. Rigid nonmetallic conduit 
shall be used only with listed fittings. Boxes and fittings 
shall comply with the applicable provisions of Article 370. 

347-16. Splices and Taps. Splices and taps shall be made 
in accordance with Section 300-15. See Article 370 for rules 
on the installation and use of boxes and conduit bodies. 



B. Construction Specifications 

347-17. General. Rigid nonmetallic conduit shall comply 
with the following. 

Marking. Each length of nonmetallic conduit shall be 
clearly and durably marked at least every 10 ft (3.05 m) as 
required in the first sentence of Section 110-21. The type 
of material shall aiso be included in the marking unless it 
is visually identifiable. For conduit recognized for use above 
ground, these markings shall be permanent. For conduit 
limited to underground use only, these markings shall be 
sufficiently durable to remain legible until the material is 



installed. Conduit shall be permitted to be surface marked 
to indicate special characteristics of the material. 

FPN: Examples of these optional markings include but are 
not limited to "LS" for limited-smoke and markings such 
as "sunlight resistant." 



Article 348 — Electrical Metallic Tubing 

A. General 

348-1. Definition. Electrical metallic tubing is a listed me- 
tallic tubing of circular cross section approved for the instal- 
lation of electrical conductors when joined together with 
listed fittings. 

348-2. Other Articles. Installations of electrical metallic 
tubing shall comply with the applicable provisions of Article 
300. 

348-4. Uses Permitted. 

(a) Exposed and Concealed. The use of listed electrical 
metallic tubing shall be permitted for both exposed and 
concealed work. 

(b) Corrosion Protection. Ferrous or nonferrous electrical 
metallic tubing, elbows, couplings, and fittings shall be per- 
mitted to be installed in concrete, in direct contact with the 
earth, or in areas subject to severe corrosive influences where 



• 



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1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 348 — ELECTRICAL METALLIC TUBING 



70-173 



protected by corrosion protection and judged suitable for 
the condition. 

FPN: See Section 300-6 for information on protection 
against corrosion. 

348-5. Uses Not Permitted. Electrical metallic tubing shall 
not be used 

(1) Where, during installation or afterward, it will be subject 
to severe physical damage. 

(2) Where protected from corrosion solely by enamel. 

(3) In cinder concrete or cinder fill where subject to perma- 
nent moisture unless protected on all sides by a layer 
of noncinder concrete at least 2 in. (50.8 mm) thick or 
unless the tubing is at least 18 in. (457 mm) under the 
fill. 

(4) In any hazardous (classified) location except as permit- 
ted by Sections 502-4, 503-3, and 504-20. 

(5) For the support of fixtures or other equipment except 
conduit bodies no larger than the largest trade size of the 
tubing. Where practicable, dissimilar metals in contact 
anywhere in the system shall be avoided to eliminate 
the possibility of galvanic action. 

Exception: Aluminum fittings and enclosures shall be per- 
mitted to be used with steel electrical metallic tubing. 

B. Installation 

348-6. Wet Locations. All supports, bolts, straps, screws, 
etc., shall be of corrosion-resistant materials or protected 
against corrosion by corrosion-resistant materials. 

FPN: See Section 300-6 for information on protection 
against corrosion. 

348-7. Size. 

(a) Minimum. Tubing smaller than Vi-'m. electrical trade 
size shall not be used. 

Exception: For enclosing the leads of motors as permitted 
in Section 430- 145(b). 

(b) Maximum. The maximum size of tubing shall be the 
4-in. electrical trade size. 

FPN: Metric trade numerical designations for electrical me- 
tallic tubing are the same as those found in Extra-heavy 
Duty Rigid Steel Conduits for Electrical Installations, TEC 
981-1989; namely, Vi = 16, 3 / 4 = 21, 1 = 27, VA = 35, VA 
= 41, 2 = 53, 2l/ 2 = 63, 3 = 78, VA = 91, and 4 = 103. 

348-8. Number of Conductors in Tubing. The number of 
conductors permitted. in a single tubing shall not exceed the 
percentage fill specified in Table 1, Chapter 9. 



348-9. Reaming and Threading. Electrical metallic tub- 
ing shall not be threaded. Where integral couplings are uti- 
lized, such couplings shall be permitted to be factory 
threaded. 

All cut ends of electrical metallic tubing shall be reamed 
or otherwise finished to remove rough edges. 

348-10. Couplings and Connectors. Couplings and con- 
nectors used with tubing shall be made up tight. Where 
buried in masonry or concrete, they shall be concretetight 
type. Where installed in wet locations, they shall be of the 
raintight type. 

348-11. Bends — How Made. Bends in the tubing shall 
be made so that the tubing will not be damaged and the 
internal diameter of the tubing will not be effectively re- 
duced. The radius of the curve of the inner edge of any field 
bend shall not be less than shown in Table 346-10. 

Exception: For field bends made with a bending machine 
designed for the purpose, the minimum radius shall not be 
less than indicated in Table 346-10, Exception. 

348-12. Bends — Number in One Run. There shall not 
be more than the equivalent of four quarter bends (360 
degrees total) between pull points, e.g., conduit bodies and 
boxes. 



348-13. Supports. Electrical metallic tubing shall be in- 
stalled as a complete system as provided in Article 300. 
Each tubing length shall be securely fastened in place at 
least every 10 ft (3.05 m). In addition, each tube shall be 
securely fastened within 3 ft (914 mm) of each outlet box, 
junction box, device box, cabinet, conduit body, or other 
tubing terminations. 

Exception No. 1: Fastening of unbroken lengths shall be 
permitted to be increased to a distance of 5 ft (1.52 m) where 
structural members do not readily permit fastening within 
3 ft (914 mm). 

Exception No. 2: For concealed work in finished buildings 
or prefinished wall panels where such securing is impracti- 
cable, unbroken lengths (without coupling) of electrical me- 
tallic tubing shall be permitted to be fished. 

Horizontal runs of electrical metallic tubing supported 
by openings through framing members at intervals not 
greater than 10 ft (3.05 m) and securely fastened within 3 ft 
(914 mm) of termination points shall be permitted. 

348-14. Boxes and Fittings. Boxes and fittings shall com- 
ply with the applicable provisions of Article 370. 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-174 



ARTICLE 349 — FLEXIBLE METALLIC TUBING 



348-15. Splices and Taps. Splices and taps shall be made 
in accordance with Section 300-15. See Article 370 for rules 
on the installation and use of boxes and conduit bodies. 



C. Construction Specifications 

348-16. General. Electrical metallic tubing shall comply 
with (a) through (d). 

(a) Cross Section. The tubing, and elbows and bends for 
use with the tubing, shall have a circular cross section. 

(b) Finish. Tubing shall have such a finish or treatment of 
outer surfaces as will provide an approved durable means of 
readily distinguishing it, after installation, from rigid metal 
conduit. 

(c) Connectors. Where the tubing is coupled together by 
threads, the connector shall be designed so as to prevent 
bending of the tubing at any part of the thread. 

(d) Marking. Electrical metallic tubing shall be clearly and 
durably marked at least every 10 ft (3.05 m) as required in 
the first sentence of Section 110-21. 



Article 349 — Flexible Metallic l\ibing 

A. General 

349-1. Scope. The provisions of this article apply to a race- 
way for electric conductors that is circular in cross section, 
flexible, metallic, and liquidtight without a nonmetallic 
jacket. 

349-2. Definition. Flexible metallic tubing is a listed tub- 
ing that is circular in cross section, flexible, metallic, and 
liquidtight without a nonmetallic jacket. 

349-3. Other Articles. Installations of flexible metallic 
tubing shall comply with the provisions of the applicable 
sections of Article 300 and Section 110-21. 

349-4. Uses Permitted. Flexible metallic tubing shall be 
permitted to be used for branch circuits 

(1) In dry locations, 

(2) Where concealed, 

(3) In accessible locations, and 

(4) For system voltages of 1000 volts maximum. 

349-5. Uses Not Permitted. Flexible metallic tubing shall 
not be used 

(1) In hoistways; 

(2) In storage battery rooms; 



(3) In hazardous (classified) locations unless otherwise per- 
mitted under other articles in this Code; 

(4) Underground for direct earth burial, or embedded in 
poured concrete or aggregate; 

(5) Where subject to physical damage; and 

(6) In lengths over 6 ft (1.83 m). 

B. Construction and Installation 
349-10. Size. 

(a) Minimum. Flexible metallic tubing smaller than !/2-in. 
electrical trade size shall not be used. 

Exception No. 1: Flexible metallic tubing of Vs-in: trade 
size shall be permitted to be installed in accordance with 
Sections 300-22(b) and (c). 

Exception No. 2: Flexible metallic tubing Vs-in. trade size 
shall be permitted in lengths not in excess of 6 ft (1.83 m) 
as part of an approved assembly or for lighting fixtures. See 
Section 410-67 {c). 

(b) Maximum. The maximum size of flexible metallic tub- 
ing shall be the %-in. trade size. 

FPN: Metric trade numerical designations for flexible me- 
tallic tubing are 3 /s = 12, Vi = 16, and 3 / 4 = 21. 

349-12. Number of Conductors. 

(a) Flexible Metallic Tubing — Vi-m. and 3 /4-in. Trade 
Size. The number of conductors permitted in '/2-in. and 
3 /4-in. trade sizes of flexible metallic tubing shall not exceed 
the percentage of fill specified in Table 1, Chapter 9. 

(b) Flexible Metallic Tubing — 3 /s-in. Trade Size. The 

number of conductors permitted in 3 /8-in. trade size flexible 
metallic tubing shall not exceed that permitted in Table 
350-12. 

349-16. Grounding. See Section 250-118(8) for rules on 
the use of flexible metallic tubing as an equipment grounding 
conductor. 

349-17. Splices and Taps. Splices and taps shall be made 
in accordance with Section 300-15. See Article 370 for rules 
on the installation and use of boxes and conduit bodies. 

349-18. Fittings. Flexible metallic tubing shall be used 
only with listed terminal fittings. Fittings shall effectively 
close any openings in the connection. 

349-20. Bends. 

(a) Infrequent Flexing Use. Where the flexible metallic 
tubing shall be infrequently flexed in service after installa- 



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1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 350 — FLEXIBLE METAL CONDUIT 



70-175 



tion, the radii of bends measured to the inside of the bend 
shall not be less than specified in Table 349-20(a). 

Table 349-20(a). Minimum Radii for Flexing Use 



Trade Size 
(in.) 



Minimum Radii 
(in.) 



10 

12'/2 
171/2 



Note: For SI units, 1 in. = 25.4 mm (radii). 

(b) Fixed Bends. Where the flexible metallic tubing is bent 
for installation purposes and is not flexed or bent as required 
by use after installation, the radii of bends measured to the 
inside of the bend shall not be less than specified in Table 
349-20(b). 

Table 349-20(b). Minimum Radii for Fixed Bends 



Trade Size 
(in.) 




Minimum Radii 
(in.) 


3 /8 
Vl 






3'/2 

4 
5 


Note: For SI units, 1 in. = 


25.4 


mm 


(radii). 



Article 350 — Flexible Metal Conduit 

A. General 

350-1. Scope. This article covers the use and installation 
of flexible metal conduit and associated fittings. 

350-2. Definition. Flexible metal conduit is a raceway of 
circular cross section made of helically wound, formed, inter- 
locked metal strip. 

350-3. Other Articles. Installations of flexible metal con- 
duit shall comply with the applicable provisions of Article 
300. 

350-4. Uses Permitted. Flexible metal conduit shall be 
listed and shall be permitted to be used in exposed and 
concealed locations. 

350-5. Uses Not Permitted. Flexible metal conduit shall 
not be used in the following: 

(1) In wet locations unless the conductors are approved for 
the specific conditions and the installation is such that 



liquid is not likely to enter raceways or enclosures to 
which the conduit is connected 

(2) In hoistways, other than as permitted in Section 620- 
21(a)(1) 

(3) In storage-battery rooms 

(4) In any hazardous (classified) location other than as per- 
mitted in Sections 501 -4(b) and 504-20 

(5) Where exposed to materials having a deteriorating effect 
on the installed conductors, such as oil or gasoline 

(6) Underground or embedded in poured concrete or aggre- 
gate 

(7) Where subject to physical damage 

B. Installation 
350-10. Size. 

(a) Minimum. Flexible metal conduit less than Vi-'m. elec- 
trical trade size shall not be used unless permitted in (1) 
through (5) below for 3 /s-in. electrical trade size. 

(1) For enclosing the leads of motors as permitted in Section 
430-145(b) 

(2) In lengths not in excess of 6 ft (1.83 m) 

(a) For utilizing equipment, or 

(b) As part of a listed assembly, or 

(c) For tap connections to lighting fixtures as permitted 
in Section 410-67(c) 

(3) For manufactured wiring systems as permitted in Section 
604-6(a) 

(4) In hoistways, as permitted in Section 620-2 1(a)(1) 

(5) As part of a listed assembly to connect wired fixture 
sections as permitted in Section 41 0-77 (c) 

(b) Maximum. Flexible metal conduit larger than 4-in. 
electrical trade size shall not be used. 

FPN: Metric trade numerical designations for flexible metal 
conduit are 3 /s = 12, Vi = 16, 3 A = 21, 1 = 27, VA = 35, 
VA = 41, 2 = 53, 2Vi = 63, 3 = 78, 3'/ 2 = 91, and 4 = 
103. 

350-12. Number of Conductors. The number of conduc- 
tors permitted in a flexible metal conduit shall not exceed 
the percentage of fill specified in Table 1 , Chapter 9, or as 
permitted in Table 350-12 for 3 /s-in. flexible metal conduit. 

350-14. Grounding. Flexible metal conduit shall be per- 
mitted as a grounding means as covered in Section 250-1 18. 
Where an equipment bonding jumper is required around 
flexible metal conduit, it shall be installed in accordance 
with Section 250-102. 

Where used to connect equipment where flexibility is 
required, an equipment grounding conductor shall be in- 
stalled. 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-176 ARTICLE 351 — LIQUIDTIGHT FLEXIBLE METAL CONDUIT AND LIQUIDTIGHT FLEXIBLE NONMETALLIC CONDUIT 



Table 350-12. Maximum Number of Insulated Conductors in %-in. Flexible Metal Conduit* 











Types 


TF, XHHW, 


Types TFN, 


THHN, 


Types 


FEP, FEPB, 




Types 
Fittings 


RFH-2 


, SF-2 
Fittings 




AF, TW 






THWN 


PF, PGF 




Fittings 




Fittings 


Fittings 




Fittings 


Fittings 


Fittings 


Size 


Inside 




Outside 


Inside 




Outside 


Inside 




Outside 


Inside 


Outside 


(AWG) 


Conduit 




Conduit 


Conduit 




Conduit 


Conduit 




Conduit 


Conduit 


Conduit 


18 


2 




3 


3 




5 


5 




8 


5 


8 


16 


1 




2 


3 




4 


4 




6 


4 


6 


14 


1 




2 


2 




3 


3 




4 


3 


4 


12 


— 




— 


1 




2 


2 




3 


2 


3 


10 


— 




— 


1 




1 


1 




1 


1 


2 



• 



*In addition, one covered or bare equipment grounding conductor of the same size shall be permitted. 



350-16. Bends. There shall not be more than the equivalent 
of four quarter bends (360 degrees total) between pull points, 
e.g., conduit bodies and boxes. Bends in the conduit shall 
be made so that the conduit will not be damaged and the 
internal diameter of the conduit will not be effectively re- 
duced. The radius of the curve of the inner edge of any field 
bend shall not be less than shown in Table 346-10. 

350-18. Supports. Flexible metal conduit shall be securely 
fastened in place by an approved means within 12 in. 
(305 mm) of each box, cabinet, conduit body, or other con- 
duit termination and shall be supported and secured at inter- 
vals not to exceed 4 l /2 ft (1.37 m). 

Exception No. 1: Where flexible metal conduit is fished. 

Exception No. 2: Lengths not exceeding 3 ft (914 mm) at 
terminals where flexibility is required. 

Exception No. 3: Lengths not exceeding 6 ft (1.83 m) from 
a fixture terminal connection for tap connections to light 
fixtures as permitted in Section 410-67(c). 

Horizontal runs of flexible metal conduit supported by 
openings through framing members at intervals not greater 
than AVi ft (1.37 m) and securely fastened within 12 in. 
(305 mm) of termination points shall be permitted. 

350-20. Fittings. Fittings used with flexible metal conduit 
shall be listed. Angle connectors shall not be used for con- 
cealed raceway installations. 

350-22. Trimming. All cut ends of flexible metal conduit 
shall be trimmed or otherwise finished to remove rough 
edges, except where fittings that thread into the convolutions 
are used. 

350-24. Splices and Taps. Splices and taps shall be made 
in accordance with Section 300-15. See Article 370 for rules 
on the installation and use of boxes and conduit bodies. 



Article 351 — Liquidtight Flexible Metal Conduit 
and Liquidtight Flexible Nonmetallic Conduit 

351-1. Scope. This article covers liquidtight flexible metal 
conduit and liquidtight flexible nonmetallic conduit. 

A. Liquidtight Flexible Metal Conduit 

351-2. Definition. Liquidtight flexible metal conduit is a 
listed raceway of circular cross section having an outer liq- 
uidtight, nonmetallic, sunlight-resistant jacket over an inner 
flexible metal core with associated couplings, connectors, 
and fittings and approved for the installation of electric 
conductors. 

351-3. Other Articles. Installations of liquidtight flexible 
metal conduit shall comply with the applicable provisions 
of Article 300 and with the specific sections of Articles 350, 
501, 502, 503, and 553 referenced below. 

FPN: For marking requirements, see Section 110-21. 

351-4. Use. 

(a) Permitted. Listed liquidtight flexible metal conduit 
shall be permitted to be used in exposed or concealed loca- 
tions as follows: 

(1) Where conditions of installation, operation, or mainte- 
nance require flexibility or protection from liquids, va- 
pors,, or solids 

(2) As permitted by Sections 501 -4(b), 502-4, 503-3, and 
504-20 and in other hazardous (classified) locations 
where specifically approved, and by Section 553-7(b) 

(3) For direct burial where listed and marked for the purpose 

(b) Not Permitted. Liquidtight flexible metal conduit shall 
not be used as follows: 

(1) Where subject to physical damage 

(2) Where any combination of ambient and conductor tern- 



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ARTICLE 351 — LIQUIDTIGHT FLEXIBLE METAL CONDUIT AND LIQUIDTIGHT FLEXIBLE NONMETALLIC CONDUIT 70-177 



perature will produce an operating temperature in excess 
of that for which the material is approved 

351-5. Size. 

(a) Minimum. Liquidtight flexible metal conduit smaller 
than '/2-in. electrical trade size shall not be used. 

Exception: Liquidtight flexible metal conduit of Vs-in. size 
shall be permitted as covered in Section 350-10(a). 

(b) Maximum. The maximum size of liquidtight flexible 
metal conduit shall be the 4-in. trade size. 

FPN: Metric trade numerical designations for liquidtight 
flexible metal conduit are 3 /s = 12, Vi = 16, 3 /4 = 21, 1 = 
27, VA = 35, Wi = 41, 2 = 53, 2 l A = 63, 3 = 78, 3Vi = 
91, and 4 = 103. 



around liquidtight flexible metal conduit, it shall be installed 
in accordance with Section 250-102. 

Where used to connect equipment where flexibility is 
required, an equipment grounding conductor shall be in- 
stalled. 

FPN: See Sections 501-16(b), 502-16(b), and 503-16(b) for 
types of equipment grounding conductors. 

351-10. Bends — Number in One Run. There shall not 
be more than the equivalent of four quarter bends (360 
degrees total) between pull points, e.g., conduit bodies and 
boxes. 

351-11. Splices and Taps. Splices and taps shall be made 
in accordance with Section 300-15. See Article 370 for rules 
on the installation and use of boxes and conduit bodies. 



351-6. Number of Conductors. 

(a) Single Conduit. The number of conductors permitted 
in a single conduit, V^-in. through 4-in. trade sizes, shall not 
exceed the percentage of fill specified in Table 1, Chapter 9. 

(b) Liquidtight Flexible Metal Conduit — 3 /s-in. Size. 

The number of conductors permitted in Vs-in. liquidtight 
flexible metal conduit shall not exceed that permitted in 
Table 350-12. 

351-7. Fittings. Liquidtight flexible metal conduit shall be 
used only with listed terminal fittings. Angle connectors 
shall not be used for concealed raceway installations. 

351-8. Supports. Liquidtight flexible metal conduit shall 
be securely fastened in place by an approved means within 
12 in. (305 mm) of each box, cabinet, conduit body, or other 
conduit termination and shall be supported and secured at 
intervals not to exceed 4'/2 ft (1.37 m). 

Exception No. 1: Where liquidtight flexible metal conduit 
is fished. 

Exception No. 2: Lengths not exceeding 3 ft (914 mm) at 
terminals where flexibility is necessary. 

Exception No. 3: Lengths not exceeding 6 ft (1.83 m)from 
a fixture terminal connection for tap conductors to lighting 
fixtures as permitted in Section 410-67(c). 

Horizontal runs of liquidtight flexible metal conduit sup- 
ported by openings through framing members at intervals 
not greater than 4 l A ft (1.37 m) and securely fastened within 
12 in. (305 mm) of termination points shall be permitted. 

351-9. Grounding. Liquidtight flexible metal conduit shall 
be permitted as a grounding means as covered in Section 
250-118. Where an equipment bonding jumper is required 



B. Liquidtight Flexible Nonmetallic Conduit 

351-22. Definition. Liquidtight flexible nonmetallic con- 
duit is a listed raceway of circular cross section of various 
types as follows: 

( 1 ) A smooth seamless inner core and cover bonded together 
and having one or more reinforcement layers between 
the core and cover, designated as Type LFNC-A 

(2) A smooth inner surface with integral reinforcement 
within the conduit wall, designated as Type LFNC-B 

(3) A corrugated internal and external surface without inte- 
gral reinforcement within the conduit wall, designated 
as Type LFNC-C 

This conduit is flame resistant and, with fittings, is ap- 
proved for the installation of electrical conductors. 

351-23. Use. 

(a) Permitted. Listed liquidtight flexible nonmetallic con- 
duit shall be permitted to be used in exposed or concealed 
locations for the following purposes. 

FPN: Extreme cold may cause some types of nonmetallic 
conduits to become brittle and therefore more susceptible 
to damage from physical contact. 

(1) Where flexibility is required for installation, operation, 
or maintenance. 

(2) Where protection of the contained conductors is required 
from vapors, liquids, or solids. 

(3) For outdoor locations where listed and marked as suit- 
able for the purpose. 

FPN: For marking requirements, see Section 110-21. 

(4) For direct burial where listed and marked for the pur- 
pose. 



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70-178 



ARTICLE 352 — SURFACE METAL RACEWAYS AND SURFACE NONMETALLIC RACEWAYS 



(5) Liquidtight flexible nonmetallic conduit as defined in 
Section 351-22(2) shall be permitted to be installed in 
lengths longer than 6 ft (1.83 m) where secured in accor- 
dance with Section 351-27. 

(6) As a listed manufactured prewired assembly, !/2-in. 
through 1-in. conduit, as defined in Section 351-22(2). 

(b) Not Permitted. Liquidtight flexible nonmetallic con- 
duit shall not be used in the following: 

(1) Where subject to physical damage 

(2) Where any combination of ambient and conductor tem- 
peratures is in excess of that for which the liquidtight 
flexible nonmetallic conduit is approved 

(3) In lengths longer than 6 ft (1.83 m), except as permitted 
by Section 351-23(a)(5) or where a longer length is 
approved as essential for a required degree of flexibility 

(4) Where voltage of the contained conductors is in excess 
of 600 volts, nominal 

Exception: As permitted in Section 600- 32(a) for electric 
signs over 600 volts. 

351-24. Size. The electrical trade sizes of liquidtight flexi- 
ble nonmetallic conduit shall be in accordance with (a) or 
(b): 

(a) Vi in. to 4 in. inclusive 

(b) V& in. as permitted below 

(1) For enclosing the leads of motors as permitted in 
Section 430- 145(b) 

(2) In lengths not exceeding 6 ft (1.83 m) as part of a 
listed assembly for tap connections to lighting fix- 
tures as required in Section 410-67(c), or for utiliza- 
tion equipment 

(3) For electric sign conductors in accordance with Sec- 
tion 600-32(a) 

FPN: Metric trade numerical designations for liquidtight 
flexible nonmetallic conduit are 3 /s = 12, Vi — 16, 3 A = 21, 

1 = 27, VA *= 35, VA = 41, 2 = 53, VA = 63, 3 = 78, 
3'/ 2 = 91, and 4 = 103. 

351-25. Number of Conductors. The number of conduc- 
tors permitted in a single conduit shall be in accordance 
with the percentage fill specified in Table 1, Chapter 9. 

351-26. Fittings. Liquidtight flexible nonmetallic conduit 
shall be used only with listed terminal fittings. Angle con- 
nectors shall not be used for concealed raceway installations. 

351-27. Securing and Supporting. Liquidtight flexible 
nonmetallic conduit, as defined in Section 351-22(2), shall 



be securely fastened and supported in accordance with one 
of the following. 

(a) The conduit shall be securely fastened at intervals not 
exceeding 3 ft (914 mm) and within 12 in. (305 mm) on 
each side of every outlet box, junction box, cabinet, or fitting. 

(b) Securing and supporting of the conduit shall not be 
required where it is fished, installed in lengths not exceeding 
3 ft (914 mm) at terminals where flexibility is required, or 
where installed in lengths not exceeding 6 ft (1.83 m) from 
a fixture terminal connection for tap conductors to lighting 
fixtures as permitted in Section 410-67(c). 

(c) Horizontal runs of liquidtight flexible nonmetallic con- 
duit supported by openings through framing members at 
intervals not exceeding 3 ft (914 mm) and securely fastened 
within 12 in. (305 mm) of termination points shall be permit- 
ted. 

351-28. Equipment Grounding. Where an equipment 
grounding conductor is required for the circuits installed in 
liquidtight flexible nonmetallic conduit, it shall be permitted 
to be installed on the inside or outside of the conduit. Where 
installed on the outside, the length of the equipment ground- 
ing conductor shall not exceed 6 ft (1.83 m) and shall be 
routed with the raceway or enclosure. Fittings and boxes 
shall be bonded or grounded in accordance with Article 250. 

351-29. Splices and Taps. Splices and taps shall be made 
in accordance with Section 300-15. See Article 370 for rules 
on the installation and use of boxes and conduit bodies. 

351-30. Bends — Number in One Run. There shall not 
be more than the equivalent of four quarter bends (360 
degrees total) between pull points, e.g., conduit bodies and 
boxes. 

Article 352 — Surface Metal Raceways and Surface 
Nonmetallic Raceways 

A. Surface Metal Raceways 
352-1. Uses. 

(a) Permitted. The use of surface metal raceways shall be 
permitted in the following: 

(1) In dry locations 

(2) In Class I, Division 2 hazardous (classified) locations 
as permitted in Section 501 -4(b), Exception 

(3) Under raised floors, as permitted in Section 645-5(d)(2) 

(b) Not Permitted. The use of surface metal raceways shall 
not be permitted in the following: 



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1999 Edition 



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ARTICLE 352 — SURFACE METAL RACEWAYS AND SURFACE NONMETALLIC RACEWAYS 



70-179 



(1) Where subject to severe physical damage, unless other- 
wise approved 

(2) Where the voltage is 300 volts or more between conduc- 
tors, unless the metal has a thickness of not less than 
0.040 in. (1.016 mm) nominal 

(3) Where subject to corrosive vapors 

(4) In hoist ways 

(5) Where concealed, except as permitted in Section 352- 
1(a)(3) 

352-2. Other Articles. Surface metal raceways shall com- 
ply with the applicable provisions of Article 300. 

352-3. Size of Conductors. No conductor larger than that 
for which the raceway is designed shall be installed in surface 
metal raceway. 

352-4. Number of Conductors in Raceways. The number 
of conductors installed in any raceway shall not be greater 
than the number for which the raceway is designed. 

The derating factors of Section 3 10- 15(b)(2)(a) shall not 
apply to conductors installed in surface metal raceways 
where all of the following conditions are met: 

(1) The cross-sectional area of the raceway exceeds 4 in. 2 
(2580 mm 2 ) 

(2) The current-carrying conductors do not exceed 30 in 
number 

(3) The sum of the cross-sectional areas of all contained 
conductors does not exceed 20 percent of the interior 
cross-sectional area of the surface metal raceway 

352-5. Extension Through Walls and Floors. Surface 
metal raceways shall be permitted to pass transversely 
through dry walls, dry partitions, and dry floors if the length 
passing through is unbroken. Access to the conductors shall 
be maintained on both sides of the wall, partition, or floor. 

352-6. Combination Raceways. Where combination sur- 
face metal raceways are used both for signaling and for 
lighting and power circuits, the different systems shall be run 
in separate compartments identified by sharply contrasting 
colors of the interior finish, and the same relative position of 
compartments shall be maintained throughout the premises. 

352-7. Splices and Taps. Splices and taps shall be per- 
mitted in surface metal raceways having a removable cover 
that is accessible after installation. The conductors, including 
splices and taps, shall not fill the raceway to more than 75 
percent of its area at that point. Splices and taps in surface 
metal raceways without removable covers shall be made 
only in junction boxes. All splices and taps shall be made 
by approved methods. 



Taps of Type FC cable installed in surface metal raceway 
shall be made in accordance with Section 363-10. 

352-8. General. Surface metal raceways shall be of such 
construction as will distinguish them from other raceways. 
Surface metal raceways and their elbows, couplings, and 
similar fittings shall be designed so that the sections can be 
electrically and mechanically coupled together and installed 
without subjecting the wires to abrasion. 

Where covers and accessories of nonmetallic materials 
are used on surface metal raceways, they shall be identified 
for such use. 

352-9. Grounding. Surface metal raceway enclosures pro- 
viding a transition from other wiring methods shall have a 
means for connecting an equipment grounding conductor. 

B. Surface Nonmetallic Raceways 

352-21. Description. Part B of this article shall apply to a 
type of surface nonmetallic raceway and fittings of suitable 
nonmetallic material that is resistant to moisture and chemi- 
cal atmospheres. It shall also be flame retardant, resistant 
to impact and crushing, resistant to distortion from heat 
under conditions likely to be encountered in service, and 
resistant to low-temperature effects. Surface nonmetallic 
raceways that have limited smoke-producing characteristics 
shall be permitted to be identified with the suffix LS. 

352-22. Use. 

(a) Permitted. The use of surface nonmetallic raceways 
shall be permitted in dry locations. 

(b) Not Permitted. Surface nonmetallic raceways shall not 
be used as follows: 

(1) Where concealed 

(2) Where subject to severe physical damage 

(3) Where the voltage is 300 volts or more between conduc- 
tors, unless listed for higher voltage 

(4) In hoistways 

(5) In any hazardous (classified) location except Class I, 
Division 2 locations as permitted in Section 501 -4(b), 
Exception 

(6) Where subject to ambient temperatures exceeding those 
for which the nonmetallic raceway is listed 

(7) For conductors whose insulation temperature limitations 
would exceed those for which the nonmetallic raceway 
is listed 

352-23. Other Articles. Surface nonmetallic raceways 
shall comply with the applicable provisions of Article 300. 
Where equipment grounding is required by Article 250, a 



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70-180 



ARTICLE 352 — SURFACE METAL RACEWAYS AND SURFACE NONMETALLIC RACEWAYS 



separate equipment grounding conductor shall be installed 
in the raceway. 

352-24. Size of Conductors. No conductor larger than that 
for which the raceway is designed shall be installed in surface 
nonmetallic raceway. 

352-25. Number of Conductors in Raceways. The num- 
ber of conductors installed in any raceway shall not be 
greater than the number for which the raceway is designed. 

352-26. Combination Raceways. Where combination sur- 
face nonmetallic raceways are used both for signaling and 
for lighting and power circuits, the different systems shall 
be run in separate compartments, identified by printed legend 
or by sharply contrasting colors of the interior finish, and the 
same relative position of compartments shall be maintained 
throughout the premises. 

352-27. General. Surface nonmetallic raceways shall be 
of such construction as will distinguish them from other 
raceways. Surface nonmetallic raceways and their elbows, 
couplings, and similar fittings shall be designed so that the 
sections can be mechanically coupled together and installed 
without subjecting the wires to abrasion. 

352-28. Extension Through Walls and Floors. Surface 
nonmetallic raceways shall be permitted to pass transversely 
through dry walls, dry partitions, and dry floors if the length 
passing through is unbroken. Access to the conductors shall 
be maintained on both sides of the wall, partition, or floor. 

352-29. Splices and Taps. Splices and taps shall be permit- 
ted in surface nonmetallic raceways having a removable 
cover that is accessible after installation. The conductors, 
including splices and taps, shall not fill the raceway to more 
than 75 percent of its area at that point. Splices and taps in 
surface nonmetallic raceways without removable covers 
shall be made only in junction boxes. All splices and taps 
shall be made by approved methods. 

C. Strut-Type Channel Raceway 

352-40. Description. Part C of this article shall apply to 
strut-type channel raceways and accessories formed of metal 
that are resistant to moisture or protected by corrosion pro- 
tection and judged suitable for the condition. These channel 
raceways shall be permitted to be galvanized, stainless, 
enameled, or PVC-coated steel, or aluminum. Covers shall 
be either metallic or nonmetallic. 



(1) Where exposed 

(2) In dry locations 

(3) In locations subject to corrosive vapors where protected 
by finishes judged suitable for the condition 

(4) Where the voltage is 600 volts or less 

(5) As power poles 

(6) In Class I, Division 2 hazardous (classified) locations 
as permitted in Section 501 -4(b), Exception 

352-42. Uses Not Permitted. 

I (a) General. Strut-type channel raceways shall not be per- 
mitted to be used where concealed. 

• 

I (b) Ferrous Metal. Ferrous channel raceways and fittings 
protected from corrosion solely by enamel shall be permitted 
only indoors and in occupancies not subject to severe corro- 
sive influences. 

352-43. Other Articles. Installation of strut-type channel 
raceways shall comply with the applicable provisions of 
Articles 250 and 300. 

352-44. Size of Conductors. No conductor larger than that 
for which the raceway is listed shall be installed in strut- 
type channel raceways. 

352-45. Number of Conductors in Raceways. The num- 
ber of conductors permitted in strut-type channel raceway 
shall not exceed the percentage fill using Table 352-45 and 
applicable outside diameter (O.D.) dimensions of specific 
types and sizes of wire given in the Tables in Chapter 9. 
I The derating factors of Section 3 10- 15 (b)(2)(a) shall not 
apply to conductors installed in strut-type channel raceways 
where all of the following conditions are met: 

(1) The cross-sectional area of the raceway exceeds 4 in. 2 
(2580 mm 2 ) 

(2) The current-carrying conductors do not exceed 30 in 
number 

(3) The sum of the cross-sectional areas of all contained 

conductors does not exceed 20 percent of the interior 

cross-sectional area of the strut-type channel raceway 

• 

CA 
Formula for wire fill: N = — — 

WA 

Where: 

N = number of wires 
CA = channel area in square inches 
WA = wire area 



• 



• 



• 



352-41. Uses Permitted. The installation of listed strut- 
type channel raceways shall be permitted: 



352-46. Extensions Through Walls and Floors. It shall be 
permitted to extend unbroken lengths of strut-type channel 



1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 354 — UNDERFLOOR RACEWAYS 



70-181 



Table 352-45. Channel Size and Inside Diameter Area 



Channel 


Area 


40% 


Area* 


25% 


Area** 














Size 


in. 2 


mm 2 


in. 2 


mm 2 


in. 2 


mm 2 


l 5 /8 X W\6 


0.887 


572 


0.355 


229 


0.222 


143 


l 5 /8 X 1 


1.151 


743 


0.460 


297 


0.288 


186 


l 5 /8 X 1% 


1.677 


1076 


0.671 


433 


0.419 


270 


l 5 /8 X l 5 /8 


2.028 


1308 


0.811 


523 


0.507 


327 


l 5 /8 X 2 7 /l6 


3.169 


2045 


1.267 


817 


0.792 


511 


l 5 /8 X 3'/4 


4.308 


2780 


1.723 


1112 


1.077 


695 


l'/2 X 3/ 4 


0.849 


548 


0.340 


219 


0.212 


137 


1/2 X 1/2 


1.828 


1179 


0.731 


472 


0.457 


295 


1/2 X l 7 /8 


2.301 


1485 


0.920 


594 


0.575 


371 


1/2 X 3 


3.854 


2487 


1.542 


995 


0.964 


622 



*Raceways with external joiners shall use a 40 percent wire fill calculation 
to determine the number of conductors permitted. 
**Raceways with internal joiners shall use a 25 percent wire fill calcula- 
tion to determine the number of conductors permitted. 



raceway through walls, partitions, and floors where closure 
strips are removable from either side and the portion within 
the wall, partition, or floor remains covered. 

352-47. Support of Strut-Type Channel Raceways. 

(a) A surface mount strut-type channel raceway shall be 
secured to the mounting surface with retention straps exter- 
nal to the channel at intervals not exceeding 10 ft (3.05 m) 
and within 3 ft (914 mm) of each outlet box, cabinet, junction 
box, or other channel raceway termination. 

(b) Suspension Mount. Strut-type channel raceways shall 
be permitted to be suspension mounted in air with approved 
appropriate methods designed for the purpose at intervals 
not to exceed 10 ft (3.05 m). 

352-48. Splices and Taps. Splices and taps shall be permit- 
ted in raceways that are accessible after installation by hav- 
ing a removable cover. The conductors, including splices 
and taps, shall not fill the raceway to more than 75 percent 
of its area at that point. All splices and taps shall be made 
by approved methods. 

352-49. General. Strut-type channel raceways shall be of 
a construction that distinguishes them from other raceways. 
Raceways and their elbows, couplings, and other fittings 
shall be designed so that the sections can be electrically 
and mechanically coupled together and installed without 
subjecting the wires to abrasion. 

Where closure strips and accessories of nonmetallic mate- 
rials are used on metallic strut-type channel raceways, they 
shall be listed and identified for such use. 

352-50. Grounding. Strut-type channel raceway enclo- 
sures providing a transition to or from other wiring methods 



shall have a means for connecting an equipment grounding 
conductor. Strut-type channel raceway shall be permitted as 
an equipment grounding conductor in accordance with 
Section 250-1 18(14). Where a snap-fit metal cover for strut- 
type channel raceway is used to achieve electrical continuity 
in accordance with the listing, this cover shall not be permit- 
ted as the means for providing electrical continuity for a 
receptacle mounted in the cover. 

352-51. Marking. Each length shall be clearly and dur- 
ably identified as required in the first sentence of Section 
110-21. 



Article 353 — Multioutlet Assembly 

353-1. Other Articles. A multioutlet assembly shall com- 
ply with applicable provisions of Article 300. 

FPN: See the definition of multioutlet assembly in Article 
100. 

353-2. Use. 

(a) Permitted. The use of a multioutlet assembly shall be 
permitted in dry locations. 

(b) Not Permitted. A multioutlet assembly shall not be 
installed as follows: 

(1) Where concealed, except that it shall be permissible 
to surround the back and sides of a metal multioutlet 
assembly by the building finish or recess a nonmetallic 
multioutlet assembly in a baseboard 

(2) Where subject to severe physical damage 

(3) Where the voltage is 300 volts or more between conduc- 
tors unless the assembly is of metal having a thickness 
of not less than 0.040 in. (1.02 mm) 

(4) Where subject to corrosive vapors 

(5) In hoistways 

(6) In any hazardous (classified) locations except Class I, 
Division 2, locations as permitted in Section 501 -4(b), 
Exception. 

353-3. Metal Multioutlet Assembly Through Dry Par- 
titions. It shall be permissible to extend a metal multioutlet 
assembly through (not run within) dry partitions, if arrange- 
ments are made for removing the cap or cover on all exposed 
portions and no outlet is located within the partitions. 

Article 354 — Underfloor Raceways 

354-1. Other Articles. Underfloor raceways shall comply 
with the applicable provisions of Article 300. 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-182 



ARTICLE 354 — UNDERFLOOR RACEWAYS 



354-2. Use. 

(a) Permitted. The installation of underfloor raceways 
shall be permitted beneath the surface of concrete or other 
flooring material or in office occupancies, where laid flush 
with the concrete floor and covered with linoleum or equiv- 
alent floor covering. 

(b) Not Permitted. Underfloor raceways shall not be in- 
stalled (1) where subject to corrosive vapors or (2) in any 
hazardous (classified) locations, except as permitted by Sec- 
tion 504-20 and in Class I, Division 2 locations as permitted 
in Section 501-4(b), Exception. Unless made of a material 
judged suitable for the condition or unless corrosion protec- 
tion approved for the condition is provided, ferrous or non- 
ferrous metal underfloor raceways, junction boxes, and 
fittings shall not be installed in concrete or in areas subject 
to severe corrosive influences. 

354-3. Covering. Raceway coverings shall comply with (a) 
through (d). 

(a) Raceways Not Over 4 in. (102 mm) Wide. Half-round 
and flat-top raceways not over 4 in. (102 mm) in width shall 
have not less than 3 A in. (19 mm) of concrete or wood above 
the raceway. 

Exception: As permitted in (c) and (d) for flat-top raceways. 

(b) Raceways Over 4 in. (102 mm) Wide but Not Over 
8 in. (203 mm) Wide. Flat-top raceways over 4 in. (102 
mm) but not over 8 in. (203 mm) wide with a minimum of 
1 in. (25.4 mm) spacing between raceways shall be covered 
with concrete to a depth of not less than 1 in. (25.4 mm). 
Raceways spaced less than 1 in. (25.4 mm) apart shall be 
covered with concrete to a depth of VA in. (38 mm). 

(c) Trench-Type Raceways Flush with Concrete. Trench- 
type flush raceways with removable covers shall be permit- 
ted to be laid flush with the floor surface. Such approved 
raceways shall be designed so that the cover plates will 
provide adequate mechanical protection and rigidity equiva- 
lent to junction box covers. 

(d) Other Raceways Flush with Concrete. In office occu- 
pancies, approved metal flat-top raceways, if not over 4 in. 
(102 mm) in width, shall be permitted to be laid flush with 
the concrete floor surface, provided they are covered with 
substantial linoleum that is not less than !/i6 in. (1.59 mm) 
in thickness or with equivalent floor covering. Where more 
than one and not more than three single raceways are each 
installed flush with the concrete, they shall be contiguous 
with each other and joined to form a rigid assembly. 

354-4. Size of Conductors. No conductor larger than that 
for which the raceway is designed shall be installed in un- 
derfloor raceways. 



354-5. Maximum Number of Conductors in Race- 
way. The combined cross-sectional area of all conductors 
or cables shall not exceed 40 percent of the interior cross- 
sectional area of the raceway. 

354-6. Splices and Taps. Splices and taps shall be made 
only in junction boxes. 

For the purposes of this section, so-called loop wiring 
(continuous, unbroken conductor connecting the individual 
outlets) shall not be considered to be a splice or tap. 

Exception: Splices and taps shall be permitted in trench- 
type flush raceway having a removable cover that is acces- 
sible after installation. The conductors, including splices 
and taps, shall not fill the raceway more than 75 percent of 
its area at that point. 

354-7. Discontinued Outlets. When an outlet is aban- 
doned, discontinued, or removed, the sections of circuit con- 
ductors supplying the outlet shall be removed from the 
raceway. No splices or reinsulated conductors, such as would 
be the case with abandoned outlets on loop wiring, shall be 
allowed in raceways. 

354-8. Laid in Straight Lines. Underfloor raceways shall 
be laid so that a straight line from the center of one junction 
box to the center of the next junction box will coincide with 
the centerline of the raceway system. Raceways shall be 
firmly held in place to prevent disturbing this alignment 
during construction. 

354-9. Markers at Ends. A suitable marker shall be in- 
stalled at or near each end of each straight run of raceways 
to locate the last insert. 

354-10. Dead Ends. Dead ends of raceways shall be 
closed. 

354-13. Junction Boxes. Junction boxes shall be leveled 
to the floor grade and sealed to prevent the free entrance of 
water or concrete. Junction boxes used with metal raceways 
shall be metal and shall be electrically continuous with the 
raceways. 

354-14. Inserts. Inserts shall be leveled and sealed to pre- 
vent the entrance of concrete. Inserts used with metal race- 
ways shall be metal and shall be electrically continuous with 
the raceway. Inserts set in or on fiber raceways before the 
floor is laid shall be mechanically secured to the raceway. 
Inserts set in fiber raceways after the floor is laid shall be 
screwed into the raceway. When cutting through the raceway 
wall and setting inserts, chips and other dirt shall not be 
allowed to remain in the raceway, and tools shall be used 



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1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 356 — CELLULAR METAL FLOOR RACEWAYS 



70-183 



that are designed so as to prevent the tool from entering the 
raceway and damaging conductors that may be in place. 

354-15. Connections to Cabinets and Wall Outlets. Con- 
nections between raceways and distribution centers and wall 
outlets shall be made by means of flexible metal conduit 
where not installed in concrete, rigid metal conduit, interme- 
diate metal conduit, electrical metallic tubing, or approved 
fittings. Where a metallic underfloor raceway system pro- 
vides for the termination of an equipment grounding conduc- 
tor, rigid nonmetallic conduit, electrical nonmetallic tubing, 
or liquidtight flexible nonmetallic conduit where not in- 
stalled in concrete, shall be permitted. 



356-6. Splices and Taps. Splices and taps shall be made 
only in header access units or junction boxes. 

For the purposes of this section, so-called loop wiring 
(continuous unbroken conductor connecting the individual 
outlets) shall not be considered to be a splice or tap. 

356-7. Discontinued Outlets. When an outlet is aban- 
doned, discontinued, or removed, the sections of circuit con- 
ductors supplying the outlet shall be removed from the 
raceway. No splices or reinsulated conductors, such as would 
be the case with abandoned outlets on loop wiring, shall be 
allowed in raceways. 



Article 356 — Cellular Metal Floor Raceways 

356-1. Definitions. For the purposes of this article, a cellu- 
lar metal floor raceway shall be defined as the hollow spaces 
of cellular metal floors, together with suitable fittings, that 
may be approved as enclosures for electric conductors. A 
cell shall be defined as a single, enclosed tubular space in 
a cellular metal floor member, the axis of the cell being 
parallel to the axis of the metal floor member. A header shall 
be defined as a transverse raceway for electric conductors, 
providing access to predetermined cells of a cellular metal 
floor, thereby permitting the installation of electric conduc- 
tors from a distribution center to the cells. 

356-2. Uses Not Permitted. Conductors shall not be in- 
stalled in cellular metal floor raceways as follows: 

(1) Where subject to corrosive vapor 

(2) In any hazardous (classified) location except as permit- 
ted by Section 504-20, and in Class I, Division 2, loca- 
tions as permitted in Section 501 -4(b), Exception 

(3) In commercial garages, other than for supplying ceiling 
outlets or extensions to the area below the floor but not 
above 

FPN: See Section 300-8 for installation of conductors with 
other systems. 

356-3. Other Articles. Cellular metal floor raceways shall 
comply with the applicable provisions of Article 300. 

A. Installation 

356-4. Size of Conductors. No conductor larger than No. 
1/0 shall be installed, except by special permission. 

356-5. Maximum Number of Conductors in Raceway. 

The combined cross-sectional area of all conductors or ca- 
bles shall not exceed 40 percent of the interior cross-sectional 
area of the cell or header. 



356-8. Markers. A suitable number of markers shall be 
installed for locating cells in the future. 

356-9. Junction Boxes. Junction boxes shall be leveled to 
the floor grade and sealed against the free entrance of water 
or concrete. Junction boxes used with these raceways shall 
be of metal and shall be electrically continuous with the 
raceway. 

356-10. Inserts. Inserts shall be leveled to the floor grade 
and sealed against the entrance of concrete. Inserts shall be 
of metal and shall be electrically continuous with the race- 
way. In cutting through the cell wall and setting inserts, 
chips and other dirt shall not be allowed to remain in the 
raceway, and tools shall be used that are designed to prevent 
the tool from entering the cell and damaging the conductors. 

356-11. Connection to Cabinets and Extensions from 
Cells. Connections between raceways and distribution cen- 
ters and wall outlets shall be made by means of flexible 
metal conduit where not installed in concrete, rigid metal 
conduit, intermediate metal conduit, electrical metallic tub- 
ing, or approved fittings. Where there are provisions for the 
termination of an equipment grounding conductor, nonme- 
tallic conduit, electrical nonmetallic tubing, or liquidtight 
flexible nonmetallic conduit where not installed in concrete, 
shall be permitted. 



B. Construction Specifications 

356-12. General. Cellular metal floor raceways shall be 
constructed so that adequate electrical and mechanical con- 
tinuity of the complete system will be secured. They shall 
provide a complete enclosure for the conductors. The interior 
surfaces shall be free from burrs and sharp edges, and sur- 
faces over which conductors are drawn shall be smooth. 
Suitable bushings or fittings having smooth rounded edges 
shall be provided where conductors pass. 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-184 



ARTICLE 358 — CELLULAR CONCRETE FLOOR RACEWAYS 



Article 358 — Cellular Concrete Floor Raceways 

358-1. Scope. This article covers cellular concrete floor 
raceways, the hollow spaces in floors constructed of precast 
cellular concrete slabs, together with suitable metal fittings 
designed to provide access to the floor cells. 

358-2. Definitions. A cell shall be defined as a single, en- 
closed tubular space in a floor made of precast cellular 
concrete slabs, the direction of the cell being parallel to the 
direction of the floor member. A header shall be defined as 
transverse metal raceways for electric conductors, providing 
access to predetermined cells of a precast cellular concrete 
floor, thereby permitting the installation of electric conduc- 
tors from a distribution center to the floor cells. 

358-3. Other Articles. Cellular concrete floor raceways 
shall comply with the applicable provisions of Article 300. 

358-4. Uses Not Permitted. Conductors shall not be in- 
stalled in precast cellular concrete floor raceways as follows: 

(1) Where subject to corrosive vapor 

(2) In any hazardous (classified) locations except as permit- 
ted by Section 504-20, and in Class I, Division 2, loca- 
tions as permitted in Section 501 -4(b), Exception 

(3) In commercial garages, other than for supplying ceiling 
outlets or extensions to the area below the floor but not 
above 

FPN: See Section 300-8 for installation of conductors with 
other systems. 

358-5. Header. The header shall be installed in a straight 
line at right angles to the cells. The header shall be mechani- 
cally secured to the top of the precast cellular concrete floor. 
The end joints shall be closed by a metal closure fitting and 
sealed against the entrance of concrete. The header shall be 
electrically continuous throughout its entire length and shall 
be electrically bonded to the enclosure of the distribution 
center. 

358-6. Connection to Cabinets and Other Enclosures. 

Connections from headers to cabinets and other enclosures 
shall be made by means of listed metal raceways and listed 
fittings. 

358-7. Junction Boxes. Junction boxes shall be leveled to 
the floor grade and sealed against the free entrance of water 
or concrete. Junction boxes shall be of metal and shall be 
mechanically and electrically continuous with the header. 

358-8. Markers. A suitable number of markers shall be 
installed for the future location of cells. 



358-9. Inserts. Inserts shall be leveled and sealed against 
the entrance of concrete. Inserts shall be of metal and shall 
be fitted with grounded-type receptacles. A grounding con- 
ductor shall connect the insert receptacles to a positive 
ground connection provided on the header. Where cutting 
through the cell wall for setting inserts or other purposes 
(such as providing access openings between header and 
cells), chips and other dirt shall not be allowed to remain 
in the raceway, and the tool used shall be designed so as to 
prevent the tool from entering the cell and damaging the 
conductors. 

358-10. Size of Conductors. No conductor larger than No. 
1/0 shall be installed, except by special permission. 

358-11. Maximum Number of Conductors. The com- 
bined cross-sectional area of all conductors or cables shall 
not exceed 40 percent of the cross-sectional area of the cell 
or header. 

358-12. Splices and Taps. Splices and taps shall be made 
only in header access units or junction boxes. 

For the purposes of this section, so-called loop wiring 
(continuous unbroken conductor connecting the individual 
outlets) shall not be considered to be a splice or tap. 

358-13. Discontinued Outlets. When an outlet is aban- 
doned, discontinued, or removed, the sections of circuit con- 
ductors supplying the outlet shall be removed from the 
raceway. No splices or reinsulated conductors, such as would 
be the case of abandoned outlets on loop wiring, shall be 
allowed in raceways. 

Article 362 — Metal Wireways and Nonmetallic 
Wireways 

A. Metal Wireways 

362-1. Definition. Wireways are sheet metal troughs with 
hinged or removable covers for housing and protecting elec- 
tric wires and cable and in which conductors are laid in 
place after the wireway has been installed as a complete 
system. 

362-2. Uses. 

(a) Permitted. The use of wireways shall be permitted as 
follows: 

(1) For exposed work 

(2) In concealed spaces only in accordance with Section 
640-24 

(3) In hazardous (classified) locations as permitted by Sec- 
tion 501 -4(b) for Class I, Division 2, locations; Section 



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1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 362 — METAL WIREWAYS AND NONMETALLIC WIREWAYS 



70-185 



502-4(b) for Class II, Division 2, locations; and Section 
504-20 for intrinsically safe wiring 

Where installed in wet locations, wireways shall be listed 
for the purpose. 

I (b) Not Permitted. The use of wireways shall not be per- 
mitted where subject to severe physical damage or corrosive 
vapor. 

362-3. Other Articles. Installations of wireways shall 
comply with the applicable provisions of Article 300. 

362-4. Size of Conductors. No conductor larger than that 
for which the wireway is designed shall be installed in any 
wireway. 

362-5. Number of Conductors. Wireways shall not con- 
tain more than 30 current-carrying conductors at any cross 
section. Conductors for signaling circuits or controller con- 
ductors between a motor and its starter and used only for 
starting duty shall not be considered as current-carrying 
conductors. 

The sum of cross-sectional areas of all contained conduc- 
tors at any cross section of the wireway shall not exceed 20 
percent of the interior cross-sectional area of the wireway. 
I The derating factors specified in Section 3 10- 15(b)(2)(a) 
shall not be applicable to the 30 current-carrying conductors 
at 20 percent fill specified above. 

Exception No. 1: Where the derating factors specified in 
I Section 3 10- 15(b)(2)(a) are applied, the number of current- 
carrying conductors shall not be limited, but the sum of the 
cross-sectional areas of all contained conductors at any 
cross section of the wireway shall not exceed 20 percent of 
the interior cross-sectional area of the wireway. 

Exception No. 2: As provided in Section 520-6, the 30- 
conductor limitation shall not apply to theaters and similar 
locations. 

Exception No. 3: As provided in Section 620-32, the 20 
percent fill limitation shall not apply to elevators and dumb- 
waiters. 

362-6. Deflected Insulated Conductors. Where insulated 
conductors are deflected within a wireway, either at the ends 
or where conduits, fittings, or other raceways or cables enter 
or leave the wireway, or where the direction of the wireway 
is deflected greater than 30 degrees, dimensions correspond- 
ing to Section 373-6 shall apply. Where insulated conductors 
No. 4 or larger enter a wireway through a raceway or cable, 
the distance between those raceway and cable entries shall 
not be less than six times the trade diameter of the larger 
raceway or cable connector. 

Where insulated conductors No. 4 or larger enter a wire- 



way through a raceway or cable, the distance between race- 
way and cable entries encolsing the same conductor shall 
not be less than six times the trade diameter of the larger 
raceway or cable connector. 

362-7. Splices and Taps. Splices and taps shall be per- 
mitted within a wireway provided they are accessible. The 
conductors, including splices and taps, shall not fill the 
wireway to more than 75 percent of its area at that point. 

362-8. Supports. Wireways shall be supported in accor- 
dance with the following. 

(a) Horizontal Support. Wireways shall be supported 
where run horizontally at each end and at intervals not to 
exceed 5 ft (1.52 m) or for individual lengths longer than 
5 ft (1.52 m) at each end or joint, unless listed for other 
support intervals. The distance between supports shall not 
exceed 10 ft (3.05 m). 

(b) Vertical Support. Vertical runs of wireways shall be 
securely supported at intervals not exceeding 15 ft (4.57 m) 
and shall not have more than one joint between supports. 
Adjoining wireway sections shall be securely fastened to- 
gether to provide a rigid joint. 

362-9. Extension Through Walls. Wireways shall be per- 
mitted to pass transversely through walls if the length passing 
through the wall is unbroken. Access to the conductors shall 
be maintained on both sides of the wall. 

362-10. Dead Ends. Dead ends of wireways shall be 
closed. 

362-11. Extensions from Wireways. Extensions from 
wireways shall be made with cord pendants installed in 
accordance with Section 400-10 or any wiring method in 
Chapter 3 that includes a means for equipment grounding. 
Where a separate equipment grounding conductor is em- 
ployed, connection of the equipment grounding conductors 
in the wiring method to the wireway shall comply with 
Sections 250-8 and 250-12. Where rigid nonmetallic conduit, 
electrical nonmetallic tubing, or liquidtight flexible nonme- 
tallic conduit is used, connection of the equipment grounding 
conductor in the nonmetallic raceway to a metal wireway 
shall comply with Sections 250-8 and 250-12. 

362-12. Marking. Wireways shall be marked so that their 
manufacturer's name or trademark will be visible after instal- 
lation. 

362-13. Grounding. Grounding shall be in accordance 
with the provisions of Article 250. 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-186 



ARTICLE 362 — METAL WIREWAYS AND NONMETALLIC WIREWAYS 



B. Nonmetallic Wireways 

362-14. Definition. Nonmetallic wireways are flame-re- 
tardant, nonmetallic troughs with removable covers for hous- 
ing and protecting electric wires and cables in which 
conductors are laid in place after the wireway has been 
installed as a complete system. 

362-15. Uses Permitted. The use of listed nonmetallic 
wireways shall be permitted as follows: 

(1) Only for exposed work, except as permitted in accor- 
dance with Section 640-24 

(2) Where subject to corrosive vapors 

(3) In wet locations where listed for the purpose 

FPN: Extreme cold may cause nonmetallic wireways to be- 
come brittle and, therefore, more susceptible to damage from 
physical contact. 

362-16. Uses Not Permitted. Nonmetallic wireways shall 
not be used as follows: 

(1) Where subject to physical damage 

(2) In any hazardous (classified) location, except as permit- 
ted in Section 504-20 

(3) Where exposed to sunlight unless listed and marked as 
' suitable for the purpose 

(4) Where subject to ambient temperatures other than those 
for which nonmetallic wireway is listed 

(5) For conductors whose insulation temperature limitations 
would exceed those for which the nonmetallic wireway 
is listed 

362-17. Other Articles. Installations of nonmetallic wire- 
ways shall comply with the applicable provisions of Article 
300. Where equipment grounding is required by Article 250, 
a separate equipment grounding conductor shall be installed 
in the nonmetallic wireway. 

Exception: Where the grounded conductor is used to ground 
equipment as permitted in Section 250-142. 



shall be applicable to the current-carrying conductors up to 
and including the 20 percent fill specified above. 

362-20. Deflected Insulated Conductors. Where insu- 
lated conductors are deflected within a nonmetallic wireway, 
either at the ends or where conduits, fittings, or other race- 
ways or cables enter or leave the nonmetallic wireway, or 
where the direction of the nonmetallic wireway is deflected 
greater than 30 degrees, dimensions corresponding to Sec- 
tion 373-6 shall apply. 

362-21. Splices and Taps. Splices and taps shall be permit- 
ted within a nonmetallic wireway provided they are accessi- 
ble. The conductors, including splices and taps, shall not 
fill the nonmetallic wireway to more than 75 percent of its 
area at that point. 

362-22. Supports. Nonmetallic wireway shall be sup- 
ported in accordance with (a) and (b). 

(a) Horizontal Support. Nonmetallic wireways shall be 
supported where run horizontally at intervals not to exceed 

3 ft (914 mm), and at each end or joint, unless listed for 
other support intervals. In no case shall the distance between 
supports exceed 10 ft (3.05 m). 

(b) Vertical Support. Vertical runs of nonmetallic wire- 
way shall be securely supported at intervals not exceeding 

4 ft (1.22 m), unless listed for other support intervals, and 
shall not have more than one joint between supports. Adjoin- 
ing nonmetallic wireway sections shall be securely fastened 
together to provide a rigid joint.- 

362-23. Expansion Fittings. Expansion fittings for non- 
metallic wireway shall be provided to compensate for ther- 
mal expansion and contraction where the length change is 
expected to be 0.25 in. (6.36 mm) or greater in a straight 
run. 

I FPN: See Table 347-9 for expansion characteristics of PVC 
rigid nonmetallic conduit. The expansion characteristics of 
PVC nonmetallic wireway are identical. 



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362-18. Size of Conductors. No conductor larger than that 
for which the nonmetallic wireway is designed shall be 
installed in any nonmetallic wireway. 

362-19. Number of Conductors. The sum of cross- 
sectional areas of all contained conductors at any cross sec- 
tion of the nonmetallic wireway shall not exceed 20 percent 
of the interior cross-sectional area of the nonmetallic wire- 
way. Conductors for signaling circuits or controller conduc- 
tors between a motor and its starter and used only for starting 
duty shall not be considered as current-carrying conductors. 
The derating factors specified in Section 310-15(b)(2)(a) 



362-24. Extension Through Walls. Nonmetallic wireways 
shall be permitted to pass transversely through walls if the 
length passing through the wall is unbroken. Access to the 
conductors shall be maintained on both sides of the wall. 

362-25. Dead Ends. Dead ends of nonmetallic wireways 
shall be closed using listed fittings. 

362-26. Extensions from Nonmetallic Wireways. Exten- 
sions from nonmetallic wireways shall be made with cord 
pendants or any wiring method of Chapter 3. A separate 
equipment grounding conductor shall be installed in, or an 



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1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 363 — FLAT CABLE ASSEMBLIES: TYPE FC 



70-187 



equipment grounding connection shall be made to, any of 
the wiring methods used for the extension. 

362-27. Marking. Npnmetallic wireways shall be marked 
so that the manufacturer's name or trademark and interior 
cross-sectional area in square inches shall be visible after 
installation. Nonmetallic wireways that have limited smoke- 
producing characteristics shall be permitted to be identified 
with the suffix LS. 

Article 363 — Flat Cable Assemblies: type FC 

363-1. Definition, type FC, a- flat cable assembly, is an 
assembly of parallel conductors formed integrally with an 
insulating material web specifically designed for field instal- 
lation in surface metal raceway. 

363-2. Other Articles. In addition to the provisions of this 
article, installation of Type FC cable shall conform with the 
applicable provisions. of Articles 210, 220, 250, 300, 310, 
and 352. 

363-3. Uses Permitted. Flat cable assemblies shall be per- 
mitted only as branch circuits to supply suitable tap devices 
for lighting, small appliances, or small power loads. Flat 
cable assemblies shall be installed for exposed work only. 
Flat cable assemblies shall be installed in locations where 
they will not be subjected to severe physical damage. 

363-4. Uses Not Permitted. Flat cable assemblies shall not 
be installed in the following: 

(1) Where subject to corrosive vapors unless suitable for 
the application 

(2) In hoistways 

(3) In any hazardous (classified) location 

(4) Outdoors or in wet or damp locations unless identified 
for use in wet locations 

363-5. Installation. Flat cable assemblies shall be installed 
in the field only in surface metal raceways identified for 
the use. The channel portion of the surface metal raceway 
systems shall be installed as complete systems before the 
flat cable assemblies are pulled into the raceways. 

363-6. Number of Conductors. The flat cable assemblies 
shall consist of either two, three, or four conductors. 

363-7. Size of Conductors. Flat cable assemblies shall 
have conductors of No. 10 special stranded copper wires. 

363-8. Conductor Insulation. The entire flat cable assem- 
bly shall be formed to provide a suitable insulation covering 



all of the conductors and using one of the materials recog- 
nized in Table 310-13 for general branch-circuit wiring. 

363-9. Splices. Splices shall be made in listed junction 
boxes. 

363-10. Taps. Taps shall be made between any phase con- 
ductor and the grounded conductor or any other phase 
conductor by means of devices and fittings identified for 
the use. Tap devices shall be rated at not less than 15 amperes, 
or more than 300 volts to ground, and they shall be color- 
coded in accordance with the requirements of Section 363- 
20. 

363-11. Dead Ends. Each flat cable assembly dead end 
shall be terminated in an end-cap device identified for the 
use. 

The dead-end fitting for the enclosing surface metal race- 
way shall be identified for the use. 

363-12. Fixture Hangers. Fixture hangers installed with 
the flat cable assemblies shall be identified for the use. 

363-13. Fittings. Fittings to be installed with flat cable 
assemblies shall be designed and installed to prevent physi- 
cal damage to the cable assemblies. 

363-14. Extensions. All extensions from flat cable assem- 
blies shall be made by approved wiring methods, within 
the junction boxes, installed at either end of the flat cable 
assembly runs. 

363-15. Supports. The flat cable assemblies shall be sup- 
ported by means of their special design features, within the 
surface metal raceways. 

The surface metal raceways shall be supported as required 
for the specific raceway to be installed. 

363-16. Rating. The rating of the branch circuit shall not 
exceed 30 amperes. 

363-17. Marking. In addition to the provisions of Section 
310-11, Type FC cable shall have the temperature rating 
durably marked on the surface at intervals not exceeding 
24 in. (610 mm). 

363-18. Protective Covers. Where a flat cable assembly 
is installed less than 8 ft (2.44 m) above the floor or fixed 
working platform, it shall be protected by a metal cover 
identified for the use. 

363-19. Identification. The grounded conductor shall be 
identified throughout its length by means of a distinctive 
and durable white or natural gray marking. 



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1999 Edition 



70-188 



ARTICLE 364 — BUSWAYS 



363-20. Terminal Block Identification. Terminal blocks 
identified for the use shall have distinctive and durable mark- 
ings for color or word coding. The grounded conductor 
section shall have a white marking or other suitable designa- 
tion. The next adjacent section of the terminal block shall 
have a black marking or other suitable designation. The next 
section shall have a red marking or other suitable des- 
ignation. The final or outer section, opposite the grounded 
conductor section of the terminal block, shall have a blue 
marking or other suitable designation. 

Article 364 — Busways 

A. General Requirements 

364-1. Scope. This article covers service-entrance, feeder, 
and branch-circuit busways and associated fittings. 

364-2. Definition. For the purpose of this article, a busway 
is considered to be a grounded metal enclosure containing 
factory-mounted, bare or insulated conductors, which are 
usually copper or aluminum bars, rods, or tubes. 

FPN: For cablebus, refer to Article 365. 

364-3. Other Articles. Installations of busways shall com- 
ply with the applicable provisions of Article 300. 

364-4. Use. 

(a) Uses Permitted. Busways shall be permitted to be in- 
stalled where they are located as follows: 

(1) Located in the open and are visible, or 

(2) Installed behind access panels, provided the busways 
are totally enclosed, of nonventilating-type construction, 
and installed so that the joints between sections and at 
fittings are accessible for maintenance purposes. Where 
installed behind access panels, means of access shall be 
provided, and the following conditions shall be met: 

(a) The space behind the access panels shall not be used 
for air-handling purposes, or 

(b) Where the space behind the access panels is used 
for environmental air, other than ducts and plenums, 
there shall be no provisions for plug-in connections, 
and the conductors shall be insulated. 

(b) Uses Not Permitted. Busways shall not be installed as 
follows: 

(1) Where subject to severe physical damage or corrosive 
vapors 

(2) In hoistways 



(3) In any hazardous (classified) location, unless specifi- 
cally approved for such use 

I FPN: See Section 501 -4(b). 

(4) Outdoors or in wet or damp locations unless identified 
for such use 

Lighting busway and trolley busway shall not be installed 
less than 8 ft (2.44 m) above the floor or working platform 
unless provided with a cover identified for the purpose. 

364-5. Support. Busways shall be securely supported at 
intervals not exceeding 5 ft (1.52 m) unless otherwise de- 
signed and marked. 

364-6. Through Walls and Floors. 

(a) Walls. Unbroken lengths of busway shall be permitted 
to be extended through dry walls. 

(b) Floors. Floor penetrations shall comply with (1) and 
(2). 

(1) Busways shall be permitted to be extended vertically 
through dry floors if totally enclosed (unventilated) where 
passing through and for a minimum distance of 6 ft (1.83 m) 
above the floor to provide adequate protection from physical 
damage. 

(2) In other than industrial establishments, where a verti- 
cal riser penetrates two or more dry floors, a minimum 4-in. 
(102-mm) high curb shall be installed around all floor open- 
ings for riser busways to prevent liquids from entering 
the opening. The curb shall be installed within 12 in. 
(304.8 mm) of the floor opening. Electrical equipment shall 
be located so that it will not be damaged by liquids that are 
retained by the curb. 

FPN: See Section 300-21 for information concerning the 
spread of fire or products of combustion. 

364-7. Dead Ends. A dead end of a busway shall be closed. 

364-8. Branches from Busways. Branches from busways 
shall be permitted to be made by the following. 

(a) Branches from busways shall be made in accordance 
with Articles 331, 334, 345, 346, 347, 348, 350, 351, 352, 
and 364. Where a nonmetallic raceway is used, connection 
of equipment grounding conductors in the nonmetallic 
raceway to the busway shall comply with Sections 250-8 
and 250-12. 

(b) Suitable cord and cable assemblies approved for extra- 
hard usage or hard usage and listed bus drop cable shall 



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ARTICLE 364 — BUSWAYS 



70-189 



be permitted as branches from busways for the connection 
of portable equipment or the connection of stationary equip- 
ment to facilitate their interchange in accordance with Sec- 
tions 400-7 and 400-8 and the following, conditions. 

(1) The cord or cable shall be attached to the building by 
an approved means. 

(2) The length of the cord or cable from a busway plug-in 
device to a suitable tension take-up support device shall 
not exceed 6 ft (1.83 m). 

Exception: In industrial establishments only, where the con- 
ditions of maintenance and supervision ensure that only 
qualified persons will service the installation, lengths ex- 
ceeding 6 ft. (1.83 m) shall be permitted between the busway 
plug-in device and the tension take-up support device where 
the cord or cable is supported at intervals not exceeding 8 ft 
(2.4 m). 

(3) The cord or cable shall be installed as a vertical riser 
from the tension take-up support device to the equipment 
served. 

(4) Strain relief cable grips shall be provided for the cord 
or cable at the busway plug-in device and equipment 
terminations. 

(c) Suitable cord and cable assemblies approved for extra- 
hard usage or hard usage and listed bus drop cable shall be 
permitted as branches from trolley-type busways for the 
connection of movable equipment in accordance with Sec- 
tions 400-7 and 400-8. 

364-9. Overcurrent Protection. Overcurrent protection 
shall be provided in accordance with Sections 364-10 
through 364-13. 

364-10. Rating of Overcurrent Protection — Feeders. A 

busway shall be protected against overcurrent in accordance 
with the allowable current rating of the busway. 

Exception No. 1: The applicable provisions of Section 
240-3 shall be permitted. 

Exception No. 2: Where used as transformer secondary ties, 
the provisions of Section 450-6(a)(3) shall be permitted. 

364-11. Reduction in Ampacity Size of Busway. Overcur- 
rent protection shall be required where busways are reduced 
in ampacity. 

Exception: For industrial establishments only, omission of 
overcurrent protection shall be permitted at points where 
busways are reduced in ampacity, provided that the length 
of the busway having the smaller ampacity does not exceed 
50 ft (15.2 m) and has an ampacity at least equal to one - 
third the rating or setting of the overcurrent device next 



back on the line, and provided that such busway is free from 
contact with combustible material. 

364-12. Feeder or Branch Circuits. Where a busway is 
used as a feeder, devices or plug-in connections for tapping 
off feeder or branch circuits from the busway shall Contain 
the overcurrent devices required for the protection of the 
feeder or branch circuits. The plug-in device shall consist 
of an externally operable circuit breaker or an externally 
operable fusible switch. Where such devices are mounted 
out of reach and contain disconnecting means, suitable 
means such as ropes, chains, or sticks shall be provided for 
operating the disconnecting means from the floor. 

Exception No. 1: As permitted in Section 240-21. 
Exception No. 2: For fixed or semifixed lighting fixtures, 
where the branch-circuit overcurrent device is part of the 
fixture cord plug on cord-connected fixtures. 
Exception No. 3: Where fixtures without cords are plugged 
directly into the busway and the overcurrent device is 
mounted on the fixture. 

364-13. Rating of Overcurrent Protection — Branch Cir- 
cuits. A busway used as a branch circuit shall be protected 
against overcurrent in accordance with Section 210-20. 
Where so used, the circuit shall comply with the applicable 
requirements of Articles 210, 430, and 440. 

364-15. Marking. Busways shall be marked with the volt- 
age and current rating for which they are designed, and with 
the manufacturer's name or trademark in such manner as to 
be visible after installation. 

B. Requirements for Over 600 Volts, Nominal 

364-21. Identification. Each bus run shall be provided 
with a permanent nameplate on which the following infor- 
mation shall be provided: 

(1) Rated voltage 

(2) Rated continuous current; if bus is forced-cooled, both 
the normal forced-cooled rating and the self-cooled (not 
forced-cooled) rating for the same temperature rise shall 
be given 

(3) Rated frequency 

(4) Rated impulse withstand voltage 

(5) Rated 60-Hz withstand voltage (dry) 

(6) Rated momentary current 

(7) Manufacturer's name or trademark 

FPN: See Guide for Metal-Enclosed Bus and Calculating 
Losses in Isolated-Phase Bus, ANSI C37.23-1987 (R1991), 
for construction and testing requirements for metal-enclosed 
buses. 

364-22. Grounding. Metal-enclosed bus shall be grounded 
in accordance with Article 250. 



NATIONAL ELECTRICAL CODE 



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70-190 



ARTICLE 365 — CABLEBUS 



364-23. Adjacent and Supporting Structures. Metal- 
enclosed busways shall be installed so that temperature rise 
from induced circulating currents in any adjacent metallic 
parts will not be hazardous to personnel or constitute a fire 
hazard. 

364-24. Neutral. Neutral bus, where required, shall be 
sized to carry all neutral load current, including harmonic 
currents, and shall have adequate momentary and short- 
circuif rating consistent with system requirements. 

364-25. Barriers and Seals. Bus runs that have sections 
located both inside and outside of buildings shall have a 
vapor seal at the building wall to prevent interchange of air 
between indoor and outdoor sections. 

Exception: Vapor seals shall not be required in forced- 
cooled bus. 

Fire barriers shall be provided where fire walls, floors, 
or ceilings are penetrated. 

FPN: See Section 300-21 for information concerning the 
spread of fire or products of combustion. 

364-26. Drain Facilities. Drain plugs, filter drains, or simi- 
lar methods shall be provided to remove condensed moisture 
from low points in bus run. 

364-27. Ventilated Bus Enclosures. Ventilated bus enclo- 
sures shall be installed in accordance with Article 110, Part 
C, and Section 490-24, unless designed so that foreign ob- 
jects inserted through any opening will be deflected from 
energized parts. 

364-28. Terminations and Connections. Where bus en- 
closures terminate at machines cooled by flammable gas, 
seal-off bushings, baffles, or other means shall be provided 
to prevent accumulation of flammable gas in the bus enclo- 
sures. 

Flexible or expansion connections shall be provided in 
long, straight runs of bus to allow for temperature expansion 
or contraction, or where the bus run crosses building vibra- 
tion insulation joints. 

All conductor termination and connection hardware shall 
be accessible for installation, connection, and maintenance. 

364-29. Switches. Switching devices or disconnecting 
links provided in the bus run shall have the same momentary 
rating as the bus. Disconnecting links shall be plainly marked 
to be removable only when bus is de-energized. Switching 
devices that are not load break shall be interlocked to prevent 
operation under load, and disconnecting link enclosures shall 
be interlocked to prevent access to energized parts. 

364-30. Wiring 600 Volts or Less, Nominal. Secondary 
control devices and wiring that are provided as part of the 



metal-enclosed bus run shall be insulated by fire-retardant 
barriers from all primary circuit elements with the exception 
of short lengths of wire, such as at instrument transformer 
terminals. 

Article 365 — Cablebus 

# 

365-1. Definition. Cablebus is an assembly of insulated 
conductors with fittings and conductor terminations in a 
completely enclosed, ventilated protective metal housing. 
Cablebus is ordinarily assembled at the point of installation 
from the components furnished or specified by the manufac- 
turer in accordance with instructions for the specific' job. 
This assembly is designed to carry fault current and to with- 
stand the magnetic forces of such current. 

365-2. Use. 

(a) 600 Volts or Less. Approved cablebus shall be permit- 
ted at any voltage or current for which spaced conductors are 
rated and shall be installed for exposed work only. Cablebus 
installed outdoors or in corrosive, wet, or damp locations 
shall be identified for such use. Cablebus shall not be in- 
stalled in hoistways or hazardous (classified) locations un- 
less specifically approved for such use. Cablebus shall be 
permitted to be used for branch circuits, feeders, and ser- 
vices. 

Cablebus framework, where bonded as required by Arti- 
cle 250, shall be permitted as the equipment grounding con- 
ductor for branch circuits and feeders. 

(b) Over 600 Volts. Approved cablebus shall be permitted 
for systems in excess of 600 volts, nominal. See Section 
300-37. 

365-3. Conductors. 

(a) Types of Conductors. The current-carrying conductors 
in cablebus shall have an insulation rating of 75°C (167°F) 
Or higher of an approved type and suitable for the application 
in accordance with Articles 310 and 490. 

(b) Ampacity of Conductors. The ampacity of conductors 
in cablebus shall be in accordance with Tables 310-17 and 
310-19, or Tables 310-69 and 310-70 for installations over 
600 volts. 

(c) Size and Number of Conductors. The size and number 
of conductors shall be that for which the cablebus is de- 
signed, and in no case smaller than No. 1/0. 

(d) Conductor Supports. The insulated conductors shall 
be supported on blocks or other mounting means designed 
for the purpose. 

The individual conductors in a cablebus shall be sup- 
ported at intervals not greater than 3 ft (914 mm) for hori- 



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70-191 



zontal runs and Wi ft (457 mm) for vertical runs. Vertical 
and horizontal spacing between supported conductors shall 
not be less than one conductor diameter at the points of 
support. 

365-5. Overcurrent Protection. Cablebus shall be pro- 
tected against overcurrent in accordance with the allowable 
ampacity of the cablebus conductors in accordance with 
Section 240-3. 

Exception: Overcurrent protection shall be permitted 
in accordance with Sections 240-100 and 240-101 for over 
600 volts, nominal. 

365-6. Support and Extension Through Walls and 
Floors. 

(a) Support. Cablebus shall be securely supported at inter- 
vals not exceeding 12 ft (3.66 m). 

Exception: Where spans longer than 12 ft (3.66 m) are 
required, the structure shall be specifically designed for the 
required span length. 

(b) Transversely Routed. Cablebus shall be permitted to 
extend transversely through partitions or walls, other than 
fire walls, provided the section within the wall is continuous, 
protected against physical damage, and unventilated. 

(c) Through Dry Floors and Platforms. Except where 
firestops are required, cablebus shall be permitted to extend 
vertically through dry floors and platforms, provided the 
cablebus is totally enclosed at the point where it passes 
through the floor or platform and for a distance of 6 ft 
(1.83 m) above the floor or platform. 

(d) Through Floors and Platforms in Wet Locations. Ex- 
cept where firestops are required, cablebus shall be permitted 
to extend vertically through floors and platforms in wet 
locations where (1) there are curbs or other suitable means 
to prevent water flow through the floor or platform opening, 
and (2) where the cablebus is totally enclosed at the point 
where it passes through the floor or platform and for a 
distance of 6 ft (1.83 m) above the floor or platform. 

365-7. Fittings. A cablebus system shall include approved 
fittings for the following: 

(1) Changes in horizontal or vertical direction of the run 

(2) Dead ends 

(3) Terminations in or on connected apparatus or equipment 
or the enclosures for such equipment 

(4) Additional physical protection where required, such as 
guards where subject to severe physical damage 

365-8. Conductor Terminations. Approved terminating 
means shall be used for connections to cablebus conductors. 



365-9. Grounding. A cablebus installation shall be 
grounded and bonded in accordance with Article 250, ex- 
cluding Section 250-86, Exception No. 2. 

365-10. Marking. Each section of cablebus shall be 
marked with the manufacturer's name or trade designation 
and the maximum diameter, number, voltage rating, and 
ampacity of the conductors to be installed. Markings shall 
be located so as to be visible after installation. 

Article 370 — Outlet, Device, Pull and Junction 
Boxes, Conduit Bodies and Fittings 

A. Scope and General 

370-1. Scope. This article covers the installation and use 
of all boxes and conduit bodies used as outlet, junction, or 
pull boxes, depending on their use, and manholes and other 
electric enclosures intended for personnel entry. Cast, sheet 
metal, nonmetallic, and other boxes such as FS, FD, and 
larger boxes are not classified as conduit bodies. This article 
also includes installation requirements for fittings used to 
join raceways and to connect raceways and cables to boxes 
and conduit bodies. 

370-2. Round Boxes. Round boxes shall not be used where 
conduits or connectors requiring the use of locknuts or bush- 
ings are to be connected to the side of the box. 

370-3. Nonmetallic Boxes. Nonmetallic boxes shall be 
permitted only with open wiring on insulators, concealed 
knob-and-tube wiring, nonmetallic-sheathed cable, and non- 
metallic raceways. 

Exception No. 1: Where internal bonding means are pro- 
vided between all entries, nonmetallic boxes shall be permit- 
ted to be used with metal raceways or metal-armored cables. 

Exception No. 2: Where integral bonding means with a 
provision for attaching an equipment grounding jumper in- 
side the box are provided between all threaded entries, in 
nonmetallic boxes listed for the purpose, nonmetallic boxes 
shall be permitted to be used with metal raceways or metal- 
armored cables. 

370-4. Metal Boxes. All metal boxes shall be grounded in 
accordance with the provisions of Article 250. 

370-5. Short Radius Conduit Bodies. Conduit bodies 
such as capped elbows and service-entrance elbows enclos- 
ing conductors No. 6 or smaller, and that are only intended 
to enable the installation of the raceway and the contained 
conductors, shall not contain splices, taps, or devices and 
shall be of sufficient size to provide free space for all con- 
ductors enclosed in the conduit body. 



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70-192 



ARTICLE 370 — OUTLET, DEVICE, PULL AND JUNCTION BOXES, CONDUIT BODIES AND FITTINGS 



B. Installation 

370-15. Damp, Wet, or Hazardous (Classified) Loca- 
tions. 

(a) Damp or Wet Locations. In damp or wet locations, 
boxes, conduit bodies, and fittings shall be placed or 
equipped so as to prevent moisture from entering or accumu- 
lating within the box, conduit body, or fitting. Boxes, conduit 
bodies, and fittings installed in wet locations shall be listed 
for use in wet locations. 

FPN No. 1: For boxes in floors, see Section 370-27(b). 

FPN No. 2: For protection against corrosion, see Section 
300-6. 

(b) Hazardous (Classified) Locations. Installations in 
hazardous (classified) locations shall conform to Articles 
500 through 517. 



370-16. Number of Conductors in Outlet, Device, and 
Junction Boxes, and Conduit Bodies. Boxes and conduit 
bodies shall be of sufficient size to provide free space for 
all enclosed conductors. In no case shall the volume of the 
box, as calculated in (a), be less than the fill calculation as 
calculated in (b). The minimum volume for conduit bodies 
shall be as calculated in (c). - 

The provisions of this section shall not apply to terminal 
housings supplied with motors. (See Section 430-12.) 

Boxes and conduit bodies enclosing conductors, size No. 
4 or larger, shall also comply with the provisions of Section 
37Q-28. 

(a) Box Volume Calculations. The volume of a wiring 
enclosure (box) shall be the total volume of the assembled 
sections, and, where used, the space provided by plaster 
rings, domed covers, extension rings, etc., that are marked 
with their volume in cubic inches or are made from boxes 
the dimensions of which are listed in Table 370- 16(a). 



• 



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Table 370-16(a). Metal Boxes 



Box Dimension in Inches, 


Minimum Capacity 






Maximum Number of Conductors* 




















Trade Size, or Type 


(in. 3 ) 


No. 18 


No. 16 


No. 14 


No. 12 


No. 10 


No. 8 


No. 6 


4 X VA round or octagonal 


12.5 


8 


7 


6 


5 


5 


4 


2 


4 X VA round or octagonal 


15.5 


10 


8 


7 


6 


6 


5 


3 


4 X 2!/8 round or octagonal . 


21.5 


14 


12 


10 


9 


8 


7 


4 


4 X l l A square 


18.0 


. 12 


10 


9 


8 


7 


6 


3 


4 X VA square 


21.0 


14 


12 


10 


9 


8 


7 


4 


4 X 2Ms square 


30.3 


20 


17 


15 


13 


12 


10 


6 


4"/i6 X VA square 


25.5 


17 


14 


12 


11 


10 


8 


5 


4 u /i6 X VA square 


29.5 


19 


16 


14 


13 


11 


9 


5 


4"/i6 X 2M square 


42.0 


28 


24 


21 


18 


16 


14 


8 


3 X 2 X VA device 


7.5 


5 


4 


3 


3 


3 


2 


1 


3X2X2 device 


10.0 


6 


5 


5 


4 


4 


3 


2 


3 X 2 X 2 l A device 


10.5 


7 


6 


5 


4 


4 


3 


2 


3 X 2 X 2M? device 


12.5 


8 


7 


6 


5 


5 


4 


2 


3 X 2 X 2 3 / 4 device 


14.0 


9 


8 


7 


6 


5 


4 


2 


3 X 2 X 3M> device 


18.0 


12 


10 


9 


8 


7 


6 


3 


4 X 2 Ms X VA device 


10.3 


6 


5 


5 


4 


4 


3 


2 


4 X 2'/s X VA device 


13.0 


8 


r 1 


6 


5 


5 


4 


2 


4 X 2/s X 2M device 


14.5 


9 


8 


7 


6 


5 


4' 


2 


3 3 /4 X 2 X 2/ masonry 


14.0 


9 


8 


7 


6 


5 


4 


2 


box/gang 


















3 3 /4 X 2 X 3M masonry 


21.0 


14 


12 


10 


9 


8 


7 


4 


box/gang 


















FS — Minimum internal depth 


13.5 


9 


7- 


6 


6 


5 


4 


2 


PA single cover/gang 


















FD — Minimum internal depth 


18.0 


12 


10 


9 


8 


7 


6 


3 


2 3 /8 single cover/gang 


















FS — Minimum internal depth 


18.0 


12 


10 


9 


8 


7 


6 


3 


VA multiple cover/gang . 


















FD — Minimum internal depth 


24.0 


16 


13 


12 


10 


9 


8 


4 


2 3 /s multiple cover/gang 



















Note: For SI units, 1 in. 3 = 16.4 cm 3 . 

* Where no volume allowances are required by Sections 370- 16(b)(2) through 370- 16(b)(5). 



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ARTICLE 370 — OUTLET, DEVICE, PULL AND JUNCTION BOXES, CONDUIT BODIES AND FITTINGS 



70-193 



(1) Standard Boxes. The volumes of standard boxes 
that are not marked with a cubic inch capacity shall be as 
given in Table 370- 16(a). 

(2) Other Boxes. Boxes 100 in. 3 (1640 cm 3 ) or less, 
other than those described in Table 370- 16(a), and nonme- 
tallic boxes shall be durably and legibly marked by the 
manufacturer with their cubic inch capacity. Boxes described 
in Table 370- 16(a) that have a larger cubic inch capacity 
than is designated in the table shall be permitted to have 
their cubic inch capacity marked as required by this section. 

(b) Box Fill Calculations. The volumes in paragraphs (1) 
through (5), as applicable, shall be added together. No allow- 
ance shall be required for small fittings such as locknuts 
and bushings. 

(1) Conductor Fill. Each conductor that originates out- 
side the box and terminates or is spliced within the box shall 
be counted once, and each conductor that passes through 
the box without splice or termination shall be counted once. 
The conductor fill, in cubic inches, shall be computed using 
Table 370- 16(b). A conductor, no part of which leaves the 
box, shall not be counted. 

Exception: An equipment grounding conductor or conduc- 
tors or not over four fixture wires smaller than No. 14, or 
both, shall be permitted to be omitted from the calculations 
I where they enter a box from a domed fixture or similar 
canopy and terminate within that box. 

| Table 370-16(b). Volume Allowance Required per Conductor 





Free Space Within Box 


Size of Conductor 


for Each Conductor 


(AWG) 


(in. 3 ) 


18 


1 .50 


16 


1.75 


14 


2.00 


12 


2.25 


10 


2.50 


8 


3.00 


6 


5.00 



Note: For SI units, 1 in. 3 = 16.4 cm 3 . 

(2) Clamp Fill. Where one or more internal cable 
clamps, whether factory or field supplied, are present in the 
box, a single volume allowance in accordance with Table 
370- 16(b) shall be made based on the largest conductor 
present in the box. No allowance shall be required for a 
cable connector with its clamping mechanism outside the 
box. 

(3) Support Fittings Fill. Where one or more fixture 
studs or hickeys are present in the box, a single volume 
allowance in accordance with Table 370- 16(b) shall be made 
for each type of fitting based on the largest conductor present 
in the box. 



(4) Device or Equipment Fill. For each yoke or strap 
containing one or more devices or equipment, a double 
volume allowance in accordance with Table 370- 16(b) shall 
be made for each yoke or strap based on the largest conductor 
connected to a device(s) or equipment supported by that 
yoke or strap. 

(5) Equipment Grounding Conductor Fill. Where one 
or more equipment grounding conductors or equipment 
bonding jumpers enters a box, a single volume allowance 
in accordance with Table 370- 16(b) shall be made based on 
the largest equipment grounding conductor or equipment 
bonding jumper present in the box. Where an additional set 
of equipment grounding conductors, as permitted by Section 
250- 146(d), is present in the box, an additional volume 
allowance shall be made based on the largest equipment 
grounding conductor in the additional set. 

(c) Conduit Bodies. 

(1) General. Conduit bodies enclosing No. 6 conductors 
or smaller, other than short radius conduit bodies as de- 
scribed in Section 370-5, shall have a cross-sectional area 
not less than twice the cross-sectional area of the largest 
conduit or tubing to which it is attached. The maximum 
number of conductors permitted shall be the maximum num- 
ber permitted by Table 1 of Chapter 9 for the conduit or 
tubing to which it is attached. 

(2) With Splices, Taps, or Devices. Only those conduit 
bodies that are durably and legibly marked by the man- 
ufacturer with their cubic inch capacity shall be permitted 
to contain splices, taps, or devices. The maximum number 
of conductors shall be computed in accordance with Section 
370- 16(b). Conduit bodies shall be supported in a rigid and 
secure manner. 

370-17. Conductors Entering Boxes, Conduit Bodies, or 
Fittings. Conductors entering boxes, conduit bodies, or fit- 
tings shall be protected from abrasion and shall comply with 
(a) through (d). 

(a) Openings to Be Closed. Openings through which con- 
ductors enter shall be adequately closed. 

(b) Metal Boxes and Conduit Bodies. Where metal boxes 
or conduit bodies are installed with open wiring or concealed 
knob-and-tube wiring, conductors shall enter through insu- 
lating bushings or, in dry locations, through flexible tubing 
extending from the last insulating support and firmly secured 
to the box or conduit body. Where raceway or cable is 
installed with metal boxes or conduit bodies, the raceway 
or cable shall be secured to such boxes and conduit bodies. 

(c) Nonmetallic Boxes. Nonmetallic boxes shall be suit- 
able for the lowest temperature-rated conductor entering the 
box. Where nonmetallic boxes are used with open wiring 



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70-194 



ARTICLE 370 — OUTLET, DEVICE, PULL AND JUNCTION BOXES, CONDUIT BODIES AND FITTINGS 



or concealed knob-and-tube wiring, the conductors shall 
enter the box through individual holes. Where flexible tubing 
is used to encase the conductors, the tubing shall extend 
from the last insulating support to no less than l A in. (6.35 mm) 
inside the box. Where nonmetallic-sheathed cable is used, 
the cable assembly, including the sheath, shall extend into 
the box no less than l A in. (6.35 mm) through a nonmetallic- 
sheathed cable knockout opening. In all instances, all per- 
mitted wiring methods shall be secured to the boxes. 

Exception: Where nonmetallic-sheathed cable or under- 
ground feeder and branch-circuit cable is used with single 
gang boxes no larger than a nominal size 2 ! A in. X 4 in., 
mounted in walls or ceilings, and where the cable is fastened 
within 8 in. (203 mm) of the box measured along the sheath 
and where the sheath extends through a cable knockout no 
less than 'A in. (6.35 mm), securing the cable to the box shall 
not be required. Multiple cable entries shall be permitted in 
a single cable knockout opening. 

(d) Conductors No; 4 or Larger. Installation shall comply 
with Section 300-4(f). 

370-18. Unused Openings. Unused cable or raceway 
openings in boxes and conduit bodies shall be effectively 
closed to afford protection substantially equivalent to that 
of the wall of the box or conduit body. Metal plugs or 
plates used with nonmetallic boxes or conduit bodies shall 
be recessed at least ] A in. (6.35 mm) from the outer surface 
of the box. 

370-19. Boxes Enclosing Flush Devices. Boxes used to 
enclose flush devices shall be of such design that the devices 
will be completely enclosed on back and sides, and that 
substantial support for the devices will be provided. Screws 
for supporting the box shall not be used in attachment of 
the device contained therein. 

370-20. In Wall or Ceiling. In walls or ceilings of concrete, 
tile, or other noncombustible material, boxes shall be in- 
stalled so that the front edge of the box will not be set back 
of the finished surface more than l A in. (6.35 mm). In walls 
and ceilings constructed of .wood or other combustible mate- 
rial, boxes shall be flush with the finished surface or project 
therefrom. ■■ ♦ . 

370-21. Repairing Plaster and Drywall or Plaster- 
board. Plaster, ' drywall, or plasterboard surfaces that are 
broken or incomplete shall be repaired so there will be no 
gaps or open spaces, greater than V% in. (3.18 mm) at the 
edge of the box or fitting. - 

370-22. Exposed Surface Extensions. Surface extensions 
from a box of a concealed wiring system shall be made by 



mounting and mechanically securing a box or extension 
ring over the concealed box. Where required, equipment 
grounding shall be in accordance with Article 250. 

Exception: A surface extension shall be permitted to be 
made from the cover of a concealed box where the cover is 
designed so it is unlikely to fall off, or be removed if its 
securing means becomes loose. The wiring method shall 
be flexible and arranged so that any required grounding 
continuity is independent of the connection between the box 
and cover. 

370-23. Supports. Enclosures within the scope of this arti- 
cle shall be supported in accordance with one or more of 
the provisions in (a) through (h). 

(a) Surface Mounting. An enclosure mounted on a build- 
ing or other surface shall be rigidly and securely fastened 
in place. If the surface does not provide rigid and secure 
support, additional support in accordance with other provi- 
sions of this section shall be provided. 

(b) Structural Mounting. An enclosure supported from a 
structural member of a building or from grade shall be rigidly 
supported either directly, or by using a metal, polymeric, or 
wood brace. 

(1) Nails. Nails, where used as a fastening means, shall 
be attached by using brackets on the outside of the enclosure, 
or they shall pass through the interior within l A in. (6.35 
mm) of the back or ends of the enclosure. 

(2) Braces. Metal braces shall be protected against cor- 
rosion and formed from metal that is not less than 0.020 in. 
(508 (xm) thick uncoated. Wood braces shall have a cross 
section not less than nominal 1 in. X 2 in. Wood braces in 
wet locations shall be treated for the conditions. Polymeric 
braces shall be identified as being suitable for the use. 

(c) Mounting in Finished Surfaces. An enclosure 
mounted in a finished surface shall be rigidly secured thereto 
by clamps, anchors, or fittings identified for the application. 

(d) Suspended Ceilings. An enclosure mounted to struc- 
tural or supporting elements of a suspended ceiling shall be 
not more than 100 in. 3 (1640 cm 3 ) in size and shall be 
securely fastened in place in one of the following ways. 

(1) Framing Members. An enclosure shall be fastened 
to the framing members by mechanical means such as bolts, 
screws, or rivets, or by the use of clips or other securing 
means identified for use with the type of ceiling framing 
member(s) and enclosure(s) employed. The framing mem- 
bers shall be adequately supported and securely fastened to 
each other and to the building structure. 



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ARTICLE 370 — OUTLET, DEVICE, PULL AND JUNCTION BOXES, CONDUIT BODIES AND FITTINGS 



70-195 



(2) Support Wires. The installation shall comply with 
the provisions of Section 300-1 1(a). The enclosure shall be 
secured, Using methods identified for the purpose, to ceiling 
support wires, including any additional support wires in- 
stalled for that purpose. Support wires used for enclosure 
support shall be fastened at each end so as to be taut within 
the ceiling cavity. 

(e) Raceway Supported Enclosure, Without Devices or 
Fixtures. An enclosure that does not contain a device(s) or 
support a fixture(s) or other equipment, and is supported by 
entering raceways shall not exceed 100 in. 3 (1640 cm 3 ) in 
size. It shall have threaded entries or have hubs identified 
for the purpose: It shall be supported by two or more conduits 
threaded wrenchtight into the enclosure or hubs. Each con- 
duit shall be secured within 3 ft (914 mm) of the enclosure, 
or within 18 in. (457 mm) of the enclosure if all entries are 
on the same side. 

Exception: Rigid metal, intermediate metal, or rigid non- 
metallic conduit or electrical metallic tubing shall be per- 
mitted to support a conduit body of any size, including a 
conduit body constructed with only one conduit entry, pro- 
vided the conduit body is not larger than the largest trade 
size of the conduit or electrical metallic tubing. 

(f) Raceway Supported Enclosures, with Devices or Fix- 
tures. An enclosure that contains a device(s) or supports a 
fixture(s) or other equipment and is supported by entering 
raceways shall not exceed 100 in. 3 (1640 cm 3 ) in size. It 
shall have threaded entries or have hubs identified for the 
purpose. It shall be supported by two or more conduits 
threaded wrenchtight into the enclosure or hubs. Each con- 
duit shall be secured within 18 in. (457 mm) of the enclosure. 

Exception No. 1: Rigid metal or intermediate metal conduit 
shall be permitted to support a conduit body of any size, 
including a conduit body constructed with only one conduit 
entry, provided the conduit bodies are not larger than the 
largest trade size of the conduit. 

Exception No. 2: An unbroken length(s) of rigid or interme- 
diate metal conduit shall be permitted to support a box used 
for fixture support, or to support a wiring enclosure within 
a fixture and used in lieu of a box in accordance with Section 
300-1 5(b), where all of the following conditions are met. 

(a) The conduit is securely fastened at a point so that the 
length of conduit beyond the last point of conduit support 

. does not exceed 3 ft (914 mm). 

(b) The unbroken conduit length before the last point of 
conduit support is 12 in. (305 mm) or greater, and that 
portion of the conduit is securely fastened at some point 
not less than 12 in. (305 mm) from its last point of 
support. 



(c) Where accessible to unqualified persons, the fixture, 
measured to its lowest point, is at least 8 ft (2.44 m) 
above grade or standing area and at least 3 ft (914 mm) 
measured horizontally to the 8 ft (2.44 m) elevation 
from windows, doors, porches, fire escapes, or similar 
locations. 

(d) A fixture supported by a single conduit does not exceed 
12 in. (305 mm) in any direction from the point of conduit 
entry. 

(e) The weight supported by any single conduit does not 
exceed 20 lb (9.08 kg). 

(f) At the fixture end, the conduit(s) is threaded wrenchtight 
into the box or wiring enclosure, or into hubs identified 
for the purpose. 

(g) Enclosures in Concrete or Masonry. An enclosure 
supported by embedment shall be identified as suitably pro- 
tected from corrosion and securely embedded in concrete 
or masonry. 

(h) Pendant Boxes. An enclosure supported by a pendant 
shall comply with (1) or (2). 

(1) Flexible Cord. A box shall be supported from a 
multiconductor cord or cable in an approved manner that 
protects the conductors against strain, such as a strain-relief 
connector threaded into a box with a hub. 

(2) Conduit. A box supporting lampholders or lighting 
fixtures, or wiring enclosures within fixtures used in lieu 
of boxes in accordance with Section 300- 15(b), shall be 
supported by rigid or intermediate metal conduit stems. For 
stems longer than 18 in. (457 mm), the stems shall be con- 
nected to the wiring system with flexible fittings suitable 
for the location. At the fixture end, the conduit(s) shall be 
threaded wrenchtight into the box or wiring enclosure, or 
into hubs identified for the purpose. 

Where supported by only a single conduit, the threaded 
joints shall be prevented from loosening by the use of set- 
screws or other effective means, or the fixture, at any point, 
shall be at least 8 ft (2.44 m) above grade or standing area 
and at least 3 ft (914 mm) measured horizontally to the 
8 ft (2.44 m) elevation from windows, doors, porches, fire 
escapes, or similar locations. A fixture supported by a single 
conduit shall not exceed 12 in. (305 mm) in any horizontal 
direction from the point of conduit entry. 

370-24. Depth of Outlet Boxes. No box shall have an inter- 
nal depth of less than Vi in. (12.7 mm). Boxes intended to 
enclose flush devices shall have an internal depth of not less 
than l5 /i 6 'in. (23.8 mm). 

370-25. Covers and Canopies. In completed installations, 
each box shall have a cover, faceplate, or fixture canopy. 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-196 



ARTICLE 370 — OUTLET, DEVICE, PULL AND JUNCTION BOXES, CONDUIT BODIES AND FITTINGS 



(a) Nonmetallic or Metal Covers and Plates. Nonmetallic 
or metal covers and plates shall be permitted. Where metal 
covers or plates are used, they shall comply with the ground- 
ing requirements of Section 250-110. 

FPN: For additional grounding requirements, see Section 
410-18(a) for metal fixture canopies, and Sections 380-12 
and 410-56(d) for metal faceplates. 

(b) Exposed Combustible Wall or Ceiling Finish. Where 
a fixture canopy or pan is used, any combustible wall or 
ceiling finish exposed between the edge of the canopy or 
pan and the outlet box shall be covered with noncombustible 
material. 

(c) Flexible Cord Pendants. Covers of outlet boxes and 
conduit bodies having holes through which flexible cord 
pendants pass shall be provided with bushings designed for 
the purpose or shall have smooth, well-rounded surfaces on 
which the cords may bear. So-called hard rubber or compo- 
sition bushings shall not be used. 

370-27. Outlet Boxes. 

(a) Boxes at Lighting Fixture Outlets. Boxes used at 
lighting fixture outlets shall be designed for the purpose. At 
every outlet used exclusively for lighting, the box shall 
be designed or installed so that a lighting fixture may be 
attached. 

Exception: A wall-mounted fixture weighing not more than 
6 lb (2.72 kg) and not exceeding 16 in. (406 mm) in any 
dimension shall be permitted to be supported on other boxes, 
provided the fixture or its supporting yoke is secured to the 
box with no fewer than two No. 6 or larger screws. 

(b) Floor Boxes. Boxes listed specifically for this applica- 
tion shall be used for receptacles located in the floor. 

Exception: Where the authority having jurisdiction judges 
them free from likely exposure to physical damage, moisture, 
and dirt, boxes located in elevated floors of show windows 
and similar locations shall be permitted to be other than 
those listed for floor applications. Receptacles and covers 
shall be listed as an assembly for this type of location. 

(c) Boxes at Ceiling-Suspended (Paddle) Fan Outlets. 

Outlet boxes shall not be used as the sole support for 
ceiling-suspended (paddle) fans. 

Exception: Boxes listed for the application shall be permit- 
ted as the sole means of support. 

370-28. Pull and Junction Boxes. Boxes and conduit bod- 
ies used as pull or junction boxes shall comply with (a) 
through (d). 



Exception: Terminal housings supplied with motors shall 
comply with the provisions of Section 430-12. 

(a) Minimum Size. For raceways containing conductors of 
No. 4 or larger, and for cables containing conductors of No. 
4 or larger, the minimum dimensions of pull or junction 
boxes installed in a raceway or cable run shall comply with 
the following. 

(1) Straight Pulls. In straight pulls, the length of the 
box shall not be less than eight times the trade diameter of 
the largest raceway. 

(2) Angle or U Pulls. Where splices, or where angle or 
U pulls are made, the distance between each raceway entry 
inside the box and the opposite wall of the box shall not be 
less than six times the trade diameter of the largest raceway 
in a row. This distance shall be increased for additional 
entries by the amount of the sum of the diameters of all 
other raceway entries in the same row on the same wall of 
the box. Each row shall be calculated individually, and the 
single row that provides the maximum distance shall be 
used. 

Exception: Where a raceway or cable entry is in the wall 
of a box or conduit body opposite a removable cover, the 
distance from that wall to the cover shall be permitted to 
comply with the distance required for one wire per terminal 
in Table 373 -6(a). 

The distance between raceway entries enclosing the same 
conductor shall not be less than six times the trade diameter 
of the larger raceway. 

When transposing cable size into raceway size in (a)(1) 
and (a)(2), the minimum trade size raceway required for the 
number and size of conductors in the cable shall be used. 

(3) Boxes or conduit bodies of dimensions less than those 
required in (a)(1) and (a)(2) shall be permitted for installa- 
tions of combinations of conductors that are less than the 
maximum conduit or tubing fill (of conduits or tubing being 
used) permitted by Table 1 of Chapter 9, provided the box 
or conduit body has been approved for and is permanently 
marked with the maximum number and maximum size of 
conductors permitted. 

(b) Conductors in Pull or Junction Boxes. In pull boxes 
or junction boxes having any dimension over 6 ft (1.83 m), 
all conductors shall be cabled or racked up in an approved 
manner. 

(c) Covers. All pull boxes, junction boxes, and conduit 
bodies shall be provided with covers compatible with the 
box or conduit body construction and suitable for the condi- 
tions of use. Where metal covers are used, they shall comply 

I with the grounding requirements of Section 250-110. An 



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ARTICLE 370 — OUTLET, DEVICE, PULL AND JUNCTION BOXES, CONDUIT BODIES AND FITTINGS 



70-197 



extension from the cover of an exposed box shall comply 
with Section 370-22, Exception. 

(d) Permanent Barriers. Where permanent barriers are in- 
stalled in a box, each section shall be considered as a separate 
box. 

370-29. Conduit Bodies, Junction, Pull, and Outlet Boxes 
to Be Accessible. Conduit bodies, junction, pull, and outlet 
boxes shall be installed so that the wiring contained in them 
can be rendered accessible without removing any part of 
the building or, in underground circuits, without excavating 
sidewalks, paving, earth, or other substance that is to be 
used to establish the finished grade. 

Exception: Listed boxes shall be permitted where covered 
by gravel, light aggregate, or noncohesive granulated soil 
if their location is effectively identified and accessible for 
excavation. 



C. Construction Specifications 

370-40. Metal Boxes, Conduit Bodies, and Fittings. 

(a) Corrosion Resistant. Metal boxes, conduit bodies, and 
fittings shall be corrosion resistant or shall be well- 
galvanized, enameled, or otherwise properly coated inside 
and out to prevent corrosion. 

FPN: See Section 300-6 for limitation in the use of boxes 
and fittings protected from corrosion solely by enamel. 

(b) Thickness of Metal. Sheet steel boxes not over 100 in. 3 
(1640 cm 3 ) in size shall be made from steel not less than 
0.0625 in. (1.59 mm) thick. The wall of a malleable iron 
box or conduit body and a die-cast or permanent-mold cast 
aluminum, brass, bronze, or zinc box or conduit body shall 
not be less than Yn in. (2.38 mm) thick. Other cast metal 
boxes or conduit bodies. shall have a wall thickness not less 
than !/8 in. (3.17 mm). 

Exception No.l: Listed boxes and conduit bodies shown to 
have equivalent strength and characteristics shall be per- 
mitted to be made of thinner or other metals. 

Exception No. 2: The walls of listed short radius conduit 
bodies, as covered in Section 370-5, shall be permitted to 
be made of thinner metal. 

(c) Metal Boxes Over 100 in. 3 Metal boxes over 100 in. 3 
(1640 cm 3 ) in size shall be constructed so as to be of ample 
strength and rigidity. If of sheet steel, the metal thickness 
shall not be less than 0.053 in. (1.35 mm) uncoateci. • 

(d) Grounding Provisions. A means shall be provided in 
each metal box for the connection of an equipment grounding 
conductor. The means shall be permitted to be a tapped hole 
or equivalent. 



370-41. Covers. Metal covers shall be of the same material 
as the box or conduit body with which they are used, or 
they shall be lined with firmly attached insulating material 
that is not less than Vk.in. (0.79 mm) thick, or they shall 
be listed for the purpose. Metal covers shall be the same 
thickness as the boxes or conduit body for which they are 
used, or they shall be listed for the purpose. Covers of 
porcelain or other approved insulating materials shall be 
permitted" if of such form and thickness as to afford the 
required protection and strength. 

370-42. Bushings. Covers of outlet boxes and conduit bod- 
ies having holes through which flexible cord pendants may 
pass shall be provided with approved bushings or shall have 
smooth, well-rounded surfaces on which the cord may bear. 
Where individual conductors pass through a metal cover, a 
separate hole equipped with a bushing of suitable insulating 
material shall be provided for each conductor. Such separate 
holes shall be connected by a slot as required by Section 
300-20. 

370-43. Nonmetallic Boxes. Provisions for supports or 
other mounting means for nonmetallic boxes shall be outside 
of the box, or the box shall be constructed so as to prevent 
contact between the conductors in the box and the supporting 
screws. 

370-44. Marking. All boxes and conduit bodies, covers, 
extension rings, plaster rings, and the like shall be durably 
and legibly marked with the manufacturer's name or trade- 
mark. 



D. Manholes and Other Electric Enclosures Intended 
for Personnel Entry 

370-50. General. Electric enclosures intended for per- 
sonnel entry and specifically fabricated for this purpose shall 
be of sufficient size to provide safe work space about electric 
equipment with live parts that is likely to require examina- 
tion, adjustment, servicing, or maintenance while energized. 
They shall have sufficient size to permit ready installation 
or withdrawal of the conductors employed without damage 
to the conductors or to their insulation. They shall comply 
with the provisions of this part. 

Exception: Where electric enclosures covered by Part D of 
this article are part of an industrial wiring system operating 
under conditions of maintenance and supervision that ensure 
only qualified persons will monitor and supervise the system, 
they shall be permitted to be designed and installed in accor- 
dance with appropriate engineering practice. If required by 
the authority having jurisdiction, design documentation shall 
be provided. 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-198 



ARTICLE 370 — OUTLET, DEVICE, PULL AND JUNCTION BOXES, CONDUIT BODIES AND FITTINGS 



370-51. Strength. Manholes, vaults, and their means of 
access shall be designed under qualified engineering super- 
vision and shall withstand all loads likely to be imposed on 
the structures. 

FPN: See National Electrical Safety Code, ANSI C2-1997, 
for additional information on the loading that can be expected 
to bear on underground enclosures. 

370-52. Cabling Work Space. A clear work space not less 
than 3 ft (914 mm) wide shall be provided where cables are 
located on both sides, and not less than 2 l A ft (762 mm) 
where cables are only on one side. The vertical headroom 
shall not be less than 6 ft (1.83 m) unless the opening is 
within 1 ft (305 mm), measured horizontally, of the adjacent 
interior side wall of the enclosure. 

Exception: A manhole containing only one or more of the 
following shall be permitted to have one of the horizontal 
work space dimensions reduced to 2 ft (608 mm) where the 
other horizontal clear work space is increased so the sum 
of the two dimensions is not less than 6 ft (1.83 m): 

(a) Optical fiber cables as covered in Article 770 

(b) Power-limited fire alarm circuits supplied in accordance 
with Section 760-41 

(c) Class 2 or Class 3 remote-control and signaling circuits, 
or both, supplied in accordance with Section 725-41 

370-53. Equipment Work Space. Where electric equip : 
ment with live parts that is likely to require examination, 
adjustment, servicing, or maintenance while energized is 
installed in a manhole, vault, or other enclosure designed 
for personnel access, the work space and associated require- 
ments in Section 1 10-26 shall be met for installations oper- 
ating at 600 volts or less. Where the installation is over 600 
volts, the work space and associated requirements in Section 
110-34 shall be met. A manhole access cover that weighs 
over 100 lb (45.4 kg) shall be considered as meeting the 
requirements of Section 110-34(c). 

370-54. Bending Space for Conductors. Bending space 
for conductors operating at 600 volts or below shall be 
provided in accordance with the requirements of Section 
370-28(a). Conductors operating over 600 volts shall be 
provided with bending space in accordance with Sections 
370-7 1(a) and 370-7 1(b) as applicable. Where any horizontal 
dimension exceeds 6 ft (1.83 m), all conductors shall be 
cabled or racked up in an approved manner. 

Exception: Where Section 370-71(b) applies, each row or 
column of ducts on one wall of the enclosure shall be calcu- 
lated individually, and the single row or column that provides 
the maximum distance shall be used. 

370-55. Access to Manholes. 

(a) Dimensions. Rectangular access openings shall not be 
less than 26 in.. X 22 in. .(659 mm X 557 mm). Round 



access openings in a manhole shall not be less than 26 in. 
(659 mm) in diameter. 

Exception: A manhole that has a fixed ladder that does not 
obstruct the opening, or that contains only one or more of 
the following shall be permitted to reduce the minimum cover 
diameter to 2 ft (608 mm): 

(a) Optical fiber cables as covered in Article 770 

(b) Power-limited fire alarm circuits supplied in accordance 
with Section 760-41 

(c) Class 2 or Class 3 remote-control and signaling circuits, 
or both, supplied in accordance with Section 725-41 

(b) Obstructions. Manhole openings shall be free of pro- 
trusions that could injure personnel or prevent ready egress. 

(c) Location. Manhole openings for personnel shall be lo- 
cated where they are not directly above electric equipment 
or conductors in the enclosure. Where this is not practicable, 
either a protective barrier or a fixed ladder shall be provided. 

(d) Covers. Covers shall be over 100 lb (45.4 kg) or other- 
wise designed to require the use of tools to open. They shall 
be designed or restrained so they cannot fall into the manhole 
or protrude sufficiently to contact electrical conductors or 
equipment within the manhole- 

(e) Marking. Manhole covers shall have an identifying 
mark or logo that prominently indicates their function, such 
as "electric." 

370-56. Access to Vaults and Tunnels. 

(a) Location. Access openings for personnel shall be lo- 
cated where they are not directly above electric equipment 
or conductors in the enclosure. Other openings shall be 
permitted over equipment to facilitate installation, mainte- 
nance, or replacement of equipment. 

(b) Locks. In addition to compliance with the requirements 
of Section 110-34(c), if applicable, access openings for per- 
sonnel shall be arranged so that a person on the inside can 
exit when the access door is locked from the outside, or 
in the case of normally locking by padlock, the locking 
arrangement shall be such that the padlock can be closed 
on the locking system to prevent locking from the outside. 

370-57. Ventilation. Where manholes, tunnels, and vaults 
have communicating openings into enclosed areas used by 
the public, ventilation to open air shall be provided wherever 
practicable. 

370-58. Guarding. Where conductors or equipment, or 
both, could be contacted by objects falling or being pushed 
through a ventilating grating, both conductors and live parts 
shall be protected in accordance with the requirements of 



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ARTfCLE 373 — CABINETS, CUTOUT BOXES, AND METER SOCKET ENCLOSURES 



70-199 



Sections 110-27(a)(2) or 110-31(a)(l), depending on the 
voltage. 

370-59. Fixed Ladders. Fixed ladders shall be corrosion 
resistant. 

E. Pull and Junction Boxes for Use on Systems Over 600 
Volts, Nominal 

370-70. General. Where pull and junction boxes are used 
on systems over 600 volts, the installation shall comply with 
the provisions of Part E and also the following general 
provisions of this article: 

(1) In Part A, Sections 370-2, 370-3, and 370-4 

(2) In Part B, Sections 370-15; 370-17; 370-18; 370-20; 
370-23(a), (b), or (f); and 370-29 

(3) In Part C, Sections 370-40(a) and (c) and 370-41 

370-71. Size of Pull and Junction Boxes. Pull and junction 
boxes shall provide adequate space and dimensions for the 
installation of conductors, and they shall comply with the 
specific requirements of this section. 

Exception: Terminal housings supplied with motors shall 
comply with the provisions of Section 430-12. 

(a) For Straight Pulls. The length of the box shall not be 
less than 48 times the outside diameter, over sheath, of the 
largest shielded or lead-covered conductor or cable entering 
the box. The length shall not be less than 32 times the outside 
diameter of the largest nonshielded conductor or cable. 

(b) For Angle or U Pulls. 

(1) The distance between each cable or conductor entry 
inside the box and the opposite wall of the box shall not be 
less than 36 times the outside diameter, over sheath, of the 
largest cable or conductor. This distance shall be increased 
for additional entries by the amount of the sum of the outside 
diameters, over sheath, of all other cables or conductor en- 
tries through the same wall of the box. 

Exception No. 1: Where a conductor or cable entry is in 
the wall of a box opposite a removable cover, the distance 
from that wall to the cover shall be permitted to be not less 
than the bending radius for the conductors as provided in 
Section 300-34. 

Exception No. 2: Where cables are nonshielded and not 
lead covered, the distance of 36 times the outside diameter 
shall be permitted to be reduced to 24 times the outside 
diameter. 

(2) The distance between a cable or conductor entry and 
its exit from the box shall not be less than 36 times the 
outside diameter, over sheath, of that cable or conductor. 



Exception: Where cables are nonshielded and not lead cov- 
ered, the distance of 36 times the outside diameter shall be 
permitted to be reduced to 24 times the outside diameter. 

(c) Removable Sides. One or more sides of any pull box 
shall be removable. 

370-72. Construction and Installation Requirements. 

(a) Corrosion Protection. Boxes shall be made of material 
inherently resistant to corrosion or shall be suitably pro- 
tected, both internally and externally, by enameling, galva- 
nizing, plating, or other means. 

(b) Passing Through Partitions. Suitable bushings, 
shields, or fittings having smooth, rounded edges shall be 
provided where conductors or cables pass through partitions 
and at other locations where necessary. 

(c) Complete Enclosure. Boxes shall provide a complete 
enclosure for the contained conductors or cables. 

(d) Wiring Is Accessible. Boxes shall be installed so that 
the wiring is accessible without removing any part of the 
building. Working space shall be provided in accordance 
with Section 110-34. 

(e) Suitable Covers. Boxes shall be closed by suitable cov- 
ers securely fastened in place. Underground box covers that 
weigh over 100 lb (45.4 kg) shall be considered meeting 
this requirement. Covers for boxes shall be permanently 
marked "DANGER — HIGH VOLTAGE — KEEP OUT." 
The marking shall be on the outside of the box cover and 
shall be readily visible. Letters shall be block type and at 
least Vi in. (1 2.7 mm) in height. 

(f) Suitable for Expected Handling. Boxes and their cov- 
ers shall be capable of withstanding the handling to which 
they may likely be subjected. 

Article 373 — Cabinets, Cutout Boxes, and Meter 
Socket Enclosures 

373-1. Scope. This article covers the installation and con- 
struction specifications of cabinets, cutout boxes, and meter 
socket enclosures. 



A. Installation 

373-2. Damp, Wet, or Hazardous (Classified) 
Locations. 

(a) Damp and Wet Locations. In damp or wet locations, 
surface-type enclosures within the scope of this article shall 
be placed or equipped so as to prevent moisture or water 
from entering and accumulating within the cabinet or cutout 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-200 



ARTICLE 373 — CABINETS, CUTOUT BOXES, AND METER SOCKET ENCLOSURES 



box, and shall be mounted so there is at least ] A-m. (6.35- 
mm) airspace between the enclosure and the wall or other 
supporting surface. Enclosures installed in wet locations 
shall be weatherproof. 

Exception: Nonmetallic enclosures shall be permitted to be 
installed without the airspace on a concrete, masonry, tile, 
or similar surface. 

FPN: For protection against corrosion, see Section 300-6. 

(b) Hazardous (Classified) Locations. Installations in 
hazardous (classified) locations shall conform to Articles 
500 through 517. 

373-3. Position in Wall. In walls of concrete, tile, or other 
noncombustible material, cabinets shall be installed so that 
the front edge of the cabinet will not set back of the finished 
surface more than l A in. (6.35 mm). In walls constructed of 
wood or other combustible material, cabinets shall be flush 
with the finished surface or project therefrom. 

373-4. Unused Openings. Unused openings in enclosures 
within the scope of this article shall be effectively closed 
to afford protection substantially equivalent to that of the 
enclosures within the scope of this article. Where metal 
plugs or plates are used with nonmetallic cabinets or cutout 
boxes, they shall be recessed at least l A in. (6.35 mm) from 
the outer surface. 

373-5. Cabinets, Cutout Boxes, and Meter Socket En- 
closures. Conductors entering enclosures within the scope 
of this article shall be protected from abrasion and shall 
comply with (a) through (c). 

(a) Openings to Be Closed. Openings through which con- 
ductors enter shall be adequately closed. 

(b) Metal Cabinets, Cutout Boxes, and Meter Socket 
Enclosures. Where metal enclosures within the scope of 
this article are installed with open wiring or concealed knob- 
and-tube wiring, conductors shall enter through insulating 
bushings or, in dry locations, through flexible tubing extend- 
ing from the last insulating support and firmly secured to 
the enclosure. 

(c) Cables. Where cable is used, each cable shall be secured 
to the cabinet, cutout box, or meter socket enclosure. 

Exception: Cables with entirely nonmetallic sheaths shall 
be permitted to enter the top of a surface-mounted enclosure 
through one or more nonflexible raceways not less than 
18 in. (457 mm) or more than 10 ft (3.05 m) in length, 
provided all the following conditions are met. 

(a) Each cable is fastened within 12 in. (305 mm), measured 
along the sheath, of the outer end of the raceway. 



(b) The raceway extends directly above the enclosure and 
does not penetrate a structural ceiling. 

(c) A fitting is provided on each end of the raceway to 
protect the cable(s)from abrasion and the fittings remain 
accessible after installation. 

(d) The raceway is sealed or plugged at the outer end using 
approved means so as to prevent access to the enclosure 
through the raceway. 

(e) The cable sheath is continuous through the raceway and 
extends into the enclosure beyond the fitting not less 
than 'A in. (6.35 mm). 

(f) The raceway is fastened at its outer end and at other 
points in accordance with the applicable article. 

(g) Where installed as conduit or tubing, the allowable cable 
fill does not exceed that permitted for complete conduit 
or tubing systems by Table 1 of Chapter 9 of this Code, 
and all applicable notes thereto. 

FPN: See Table 1 in Chapter 9, including Note 9, for allow- 
able cable fill in circular raceways. See Section 310- 
15(b)(2)(a) for required ampacity reductions for multiple 
cables installed in a common raceway. 

373-6. Deflection of Conductors. Conductors at terminals 
or conductors entering or leaving cabinets or cutout boxes 
and the like shall comply with (a) through (c). 

Exception: Wire-bending space in enclosures for motor con- 
trollers with provisions for one or two wires per terminal 
shall comply with Section 430- 10(b). 

(a) Width of Wiring Gutters. Conductors shall not be de- 
flected within a cabinet or cutout box unless a gutter having 
a width in accordance with Table 373-6(a) is provided. Con- 
ductors in parallel in accordance with Section 3 10-4 shall be 
judged on the basis of the number of conductors in parallel. 

(b) Wire-Bending Space at Terminals. Wire-bending 
space at each terminal shall be provided in accordance with 
d)or(2). 

(1) Table 373-6(a) shall apply where the conductor does 
not enter or leave the enclosure through the wall opposite 
its terminal. 

(2) Table 373-6(b) shall apply where the conductor does 
enter or leave the enclosure through the wall opposite its 
terminal. 

Exception No. 1: Where the distance between the wall and 
its terminal is in accordance with Table 37 3 -6(a), a conduc- 
tor shall be permitted to enter or leave an enclosure through 
the wall opposite its terminal provided the conductor enters 
or leaves the enclosure where the gutter joins an adjacent 
gutter that has a width that conforms to Table 373-6(b) for 
that conductor. 



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ARTICLE 373 — CABINETS, CUTOUT BOXES, AND METER SOCKET ENCLOSURES 



70-201 



Table 373-6(a). Minimum Wire-Bending Space at Terminals 
and Minimum Width of Wiring Gutters in Inches 



Table 373-6(b). Minimum Wire-Bending Space at Terminals 
in Inches 



Wire Size 



Wires per Terminal 



(aw»j or 












kcmil) 


1 


2 


3 


4 


5 


14-10 


Not specified 














8-6 

4-3 
2 


l'/2 

2 

2'/2 

3 

3'/2 


— 


— 


— 


— 


— 


— 


— 


— 


1/0-2/0 


5 


7 








3/0-4/0 


4 


6 


8 


— 


— 


250 


4'/2 


6 


8 


10 


— 


300-350 


5 


8 


10 


12 


— 


400-500 


6 


8 


10 


12 


14 


600-700 


8 


10 


12 


14 


16 


750-900 


8 


12 


14 


16 


18 


1000-1250 


10 


— 


— 


— 


— 


1500-2000 


12 





— 


— 


— 



Notes: 

1. For SI units, 1 in. = 25.4 mm. 

2. Bending space at terminals shall be measured in a straight line from 
the end of the lug or wire connector (in the direction that the wire 
leaves the terminal) to the wall, barrier, or obstruction. 



Exception No. 2: A conductor not larger than 350 kcmil 
shall be permitted to enter or leave an enclosure containing 
only a meter socket(s) through the wall opposite its terminal, 
provided the distance between the terminal and the opposite 
wall is not less than that specified in Table 373-6(a) and 
the terminal is a lay-in type where the terminal is either of 
the following: 

(a) Directed toward the opening in the enclosure and is 
within a 45 degree angle of directly facing the enclosure 
wall 

(b) Directly facing the enclosure wall and offset not greater 
than 50 percent of the bending space specified in Table 
373-6(a) 

FPN: Offset is the distance measured along the enclosure 
wall from the axis of the centerline of the terminal to a line 
passing through the center of the opening in the enclosure. 

(c) Conductors No. 4 or Larger. Installation shall comply 
with Section 300-4(f). 

373-7. Space in Enclosures. Cabinets and cutout boxes 
shall have sufficient space to accommodate all conductors 
installed in them without crowding. 

373-8. Enclosures for Switches or Overcurrent Devices. 

Enclosures for switches or overcurrent devices shall not be 
used as junction boxes, auxiliary gutters, or raceways for 
conductors feeding through or tapping off to other switches 
or overcurrent devices, unless adequate space for this pur- 
pose is provided. The conductors shall not fill the wiring 



Wire Size 






Wires per 


Termial 








(AWG or 


















kcmil) 


1 


2 


3 


4 or 


More 


14-10 


Not specified 

















8 


l'/2 




— 




— 




— 




6 

4 


2 
3 




— 




— 




— 




3 
2 


3 

3'/2 




— 




— 




— 




1 


4'/2 




— 




— 




— 




1/0 


5'/2 




5/2 




7 




— 




2/0 


6 




6 




7/2 




— 




3/0 


6'/2 


0/2) 


6/2 


O/2) 


.8 




— 




4/0 


7 


(I) 


7/2 


(I/2) 


8'/2 


(/O 


— 




250 


8'/2 


(2) 


8/2 


(2) 


9 


(1) 


10 




300 


10 


(3) 


10 


(2) 


11 


(1) 


12 




350 


12 


(3) 


12 


(3) 


13 


(3) 


14 


(2) 


400 


13 


(3) 


13 


(3) 


14 


(3) 


15 


(3) 


500 


14 


(3) 


14 


(3) 


15 


(3) 


16 


(3) 


600 


15 


(3) 


16 


(3) 


18 


(3) 


19 


(3) 


700 


16 


(3) 


18 


(3) 


20 


(3) 


22 


(3) 


750 


17 


(3) 


19 


(3) 


22 


(3) 


24 


(3) 


800 


18 




20 




22 




24 




900 


19 




22 




24 




24 




1000 


20 




— 




— 




— 




1250 


22 




— 




— 




— 




1500 


24 




— 




— 




— 




1750 


24 




— 




— 




— 




2000 


24 




— 




— 




— 





Notes: 

1. For SI units, 1 in. = 25.4 mm. 

2. Bending space at terminals shall be measured in a straight line from 
the end of the lug or wire connector in a direction perpendicular to 
the enclosure wall. 

3. For removable and lay-in wire terminals intended for only one wire, 
bending space shall be permitted to be reduced by the number of inches 
shown in parentheses. 



space at any cross section to more than 40 percent of the 
cross-sectional area of the space, and the conductors, splices, 
and taps shall not fill the wiring space at any cross section 
to more than 75 percent of the cross-sectional area of that 
space. 

373-9. Side or Back Wiring Spaces or Gutters. Cabinets 
and cutout boxes shall be provided with back wiring spaces, 
gutters, or wiring compartments as required by Section 373- 
11(c) and (d). 



B. Construction Specifications 

373-10. Material. Cabinets, cutout boxes, and meter 
socket enclosures shall comply with (a) through (c). 

(a) Metal Cabinets and Cutout Boxes. Metal enclosures 
within the scope of this article shall be protected both inside 
and outside against corrosion. 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-202 



ARTICLE 374 — AUXILIARY GUTTERS 



FPN: For information on protection against corrosion, see 
Section 300-6. 

(b) Strength. The design and construction of enclosures 
within the scope of this article shall be such as to secure 
ample strength and rigidity. If constructed of sheet steel, the 
metal thickness shall not be less than 0.053 in. (1.35 mm) 
uncoated. 

(c) Nonmetallic Cabinets. Nonmetallic cabinets shall be 
listed or they shall be submitted for approval prior to instal- 
lation. 

373-11. Spacing. The spacing within cabinets and cutout 
boxes shall comply with (a) through (d). 

(a) General. Spacing within cabinets and cutout boxes 
shall be sufficient to provide ample room for the distribution 
of wires and cables placed in them, and for a separation 
between metal parts of devices and apparatus mounted 
within them as follows. 

(1) Base. Other than at points of support, there shall be 
an airspace of at least !/i6 in. (1.59 mm) between the base 
of the device and the wall of any metal cabinet or cutout 
box in which the device is mounted. 

(2) Doors. There shall be an airspace of at least 1 in. 
(25.4 mm) between any live metal part, including live metal 
parts of enclosed fuses, and the door. 

Exception: Where the door is lined with an approved insu- 
lating material or is of a thickness of metal not less than 
0.093 in. (2.36 mm) uncoated, the airspace shall not be less 
than V2 in. (12.7 mm). 

(3) Live Parts. There shall be an airspace of at least 
Vi in. (12.7 mm) between the walls, back, gutter partition, 
if of metal, or door of any cabinet or cutout box and the 
nearest exposed current-carrying part of devices mounted 
within the cabinet where the voltage does not exceed 250. 
This spacing shall be increased to at least 1 in. (25.4 mm) 
for voltages of 251 to 600, nominal. 

Exception: Where the conditions in Section 373-ll(a)(2), 
Exception, are met, the airspace for nominal voltages from 
251 to 600 shall be permitted to be not less than Vi in. (12.7 
mm). 

(b) Switch Clearance. Cabinets and cutout boxes shall be 
deep enough to allow the closing of the doors when 30- 
ampere branch-circuit panelboard switches are in any posi- 
tion, when combination cutout switches are in any position, 
or when other single-throw switches are opened as far as 
their construction will permit. 

(c) Wiring Space. Cabinets and cutout boxes that contain 
devices or apparatus connected within the cabinet or box to 



more than eight conductors, including those of branch cir- 
cuits, meter loops, feeder circuits, power circuits, and similar 
circuits, but not including the supply circuit or a continuation 
thereof, shall have back-wiring spaces or one or more side- 
wiring spaces, side gutters, or wiring compartments. 

(d) Wiring Space — Enclosure. Side-wiring spaces, side 
gutters, or side-wiring compartments of cabinets and cutout 
boxes shall be made tight enclosures by means of covers, 
barriers, or partitions extending from the bases of the devices 
contained in the cabinet, to the door, frame, or sides of the 
cabinet. 

Exception: Side-wiring spaces, side gutters, and side-wiring 
compartments of cabinets shall not be required to be made 
tight enclosures where those side spaces contain only con- 
ductors that enter the cabinet directly opposite to the devices 
where they terminate. 

Partially enclosed back-wiring spaces shall be provided 
with covers to complete the enclosure. Wiring spaces that 
are required by (c), and that are exposed when doors are 
open, shall be provided with covers to complete the enclo- 
sure. Where adequate space is provided for feed-through 
conductors and for splices as required in Section 373-8, 
additional barriers shall not be required. 

Article 374 — Auxiliary Gutters 

374-1. Use. Auxiliary gutters shall be permitted to sup- 
plement wiring spaces at meter centers, distribution centers, 
switchboards, and similar points of wiring systems and may 
enclose conductors or busbars but shall not be used to enclose 
switches, overcurrent devices, appliances, or other similar 
equipment. 

374-2. Extension Beyond Equipment. An auxiliary gutter 
shall not extend a greater distance than 30 ft (9.14 m) beyond 
the equipment that it supplements: 

Exception: As permitted in Section 620-35 for elevators, an 
auxiliary gutter shall be permitted to extend a distance 
greater than 30 ft (9.14 m) beyond the equipment that it 
supplements. 

FPN: For wireways, see Article 362. For busways, see Arti- 
cle 364. 

374-3. Supports. 

(a) Sheet Metal Auxiliary Gutters. Sheet metal auxiliary 
gutters shall be supported throughout their entire length at 
intervals not exceeding 5 ft (1.52 m). 

(b) Nonmetallic Auxiliary Gutters. Nonmetallic auxiliary 
gutters shall be supported at intervals not to exceed 3 ft 



• 



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1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 374 — AUXILIARY GUTTERS 



70-203 



(914 mm) and at each end or joint, unless listed for other 
support intervals. In no case shall the distance between sup- 
ports exceed 10 ft (3.05 m). 

374-4. Covers. Covers shall be securely fastened to the 
gutter. 

374-5. Number of Conductors. 

(a) Sheet Metal Auxiliary Gutters. The number of con- 
ductors permitted in a sheet metal auxiliary gutter shall be 
in accordance with (1) through (4). 

(1) Sheet metal auxiliary gutters shall not contain more 
than 30 current-carrying conductors at any cross section. 
Conductors for signaling circuits or controller conductors 
between a motor and its starter and used only for starting 
duty shall not be considered as current-carrying conductors. 

(2) As provided in Section 620-35 for elevators, the 30 
conductor limitation shall not apply. 

(3) The sum of the cross-sectional areas of all contained 
conductors at any cross-section of a sheet metal auxiliary 
gutter shall not exceed 20 percent of the interior cross- 
sectional area of the sheet metal auxiliary gutter. 

(4) Where the 20 percent fill specified in (3) is not ex- 
ceeded and the derating factors specified in Section 310- 
15(b)(2)(a) is applied, the number of current-carrying con- 
ductors shall not be limited. 

(b) Nonmetallic Auxiliary Gutters. The sum of cross- 
sectional areas of all contained conductors at any cross sec- 
tion of the nonmetallic auxiliary gutter shall not exceed 20 
percent of the interior cross-section area of the nonmetallic 
auxiliary gutter. 

374-6. Ampacity of Conductors. 

(a) Sheet Metal Auxiliary Gutters. Where the number of 
current-carrying conductors contained in the sheet metal 
auxiliary gutter is 30 or less, the correction factors specified 
in Section 310-15(b)(2)(a) shall not apply. The current car- 
ried continuously in bare copper bars in sheet metal auxiliary 
gutters shall not exceed 1000 amperes/in. 2 (645 mm 2 ) of 
cross section of the conductor. For aluminum bars, the cur- 
rent carried continuously shall not exceed 700 amperes/in. 2 
(645 mm 2 ) of cross section of the conductor. 

(b) Nonmetallic Auxiliary Gutters. The derating factors 
specified in Section 3 10-1 5(b)(2)(a) shall be applicable to 
the current-carrying conductors in the nonmetallic auxiliary 
gutter. 

374-7. Clearance of Bare Live Parts. Bare conductors 
shall be securely and rigidly supported so that the minimum 



clearance between bare current-carrying metal parts of dif- 
ferent potential mounted on the same surface will not be 
less than 2 in. (50.8 mm), nor less than 1 in. (25.4 mm) for 
parts that are held free in the air. A clearance not less than 
1 in. (25.4 mm) shall be secured between bare current- 
carrying metal parts and any metal surface. Adequate provi- 
sions shall be made for the expansion and contraction of 
busbars. 

374-8. Splices and Taps. Splices and taps shall comply 
with (a) through (d). 

(a) Within Gutters. Splices or taps shall be permitted 
within gutters where they are accessible by means of remov- 
able covers or doors. The conductors, including splices and 
taps, shall not fill the gutter to more than 75 percent of its 
area. 

(b) Bare Conductors. Taps from bare conductors shall 
leave the gutter opposite their terminal connections, and 
conductors shall not be brought in contact with uninsulated 
current-carrying parts of different potential. 

(c) Suitably Identified. All taps shall be suitably identified 
at the gutter as to the circuit or equipment that they supply. 

(d) Overcurrent Protection. Tap connections from con- 
ductors in auxiliary gutters shall be provided with overcur- 
rent protection as required in Section 240-21. 

374-9. Construction and Installation. Auxiliary gutters 
shall comply with (a) through (f). 

(a) Electrical and Mechanical Continuity. Gutters shall 
be constructed and installed so that adequate electrical and 
mechanical continuity of the complete system will be se- 
cured. 

(b) Substantial Construction. Gutters shall be of sub- 
stantial construction and shall provide a complete enclosure 
for the contained conductors. All surfaces, both interior and 
exterior, shall be suitably protected from corrosion. Corner 
joints shall be made tight, and where the assembly is held 
together by rivets, bolts, or screws, such fasteners shall be 
spaced not more than 12 in. (305 mm) apart. 

(c) Smooth Rounded Edges. Suitable bushings, shields, 
or fittings having smooth, rounded edges shall be provided 
where conductors pass between gutters, through partitions, 
around bends, between gutters and cabinets or junction 
boxes, and at other locations where necessary to prevent 
abrasion of the insulation of the conductors. 

(d) Deflected Insulated Conductors. Where insulated 
conductors are deflected within an auxiliary gutter, either at 
the ends or where conduits, fittings, or other raceways or 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-204 



ARTICLE 380 — SWITCHES 



cables enter or leave the gutter, or where the direction of 
the gutter is deflected greater than 30 degrees, dimensions 
corresponding to Section 373-6 shall apply. 

(e) Indoor and Outdoor Use. 

(1) Sheet Metal Auxiliary Gutters. Sheet metal auxil- 
iary gutters installed in wet locations shall be suitable for 
such locations. 

(2) Nonmetallic Auxiliary Gutters. 

(a) Nonmetallic auxiliary gutters installed outdoors shall 

(1) Be listed and marked as suitable for exposure to sunlight; 

(2) Be listed and marked as suitable for use in wet locations; 

(3) Be listed for the maximum ambient temperature of the 
installation, and marked for the installed conductor insu- 
lation temperature rating; and 

(4) Have expansion fittings installed where the expected 
length change due to expansion and contraction due to 
temperature change is more than 0.25 in. (6.35 mm). 

(b) Nonmetallic auxiliary gutters installed indoors shall 

(1) Be listed for the maximum ambient temperature of the 
installation and marked for the installed conductor insu- 
lation temperature rating, and 

(2) Have expansion fittings installed where expected length 
change, due to expansion and contraction due to temper- 
ature change, is more than Vi in. (6.35 mm). 

FPN: Extreme cold may cause nonmetallic auxiliary gutter 
to become brittle and, therefore, more susceptible to damage 
from physical contact. 

(f) Grounding. Grounding shall be in accordance with the 
provisions of Article 250. 



Article 380 — Switches 

A. Installation 

380-1. Scope. The provisions of this article shall apply to 
all switches, switching devices, and circuit breakers where 
used as switches. 

380-2. Switch Connections. 

(a) Three- Way and Four-Way Switches. Three-way and 
four-way switches shall be wired so that all switching is 
done only in the ungrounded circuit conductor. Where in 
metal raceways or metal-armored cables, wiring between 
switches and outlets shall be in accordance with Section 
300-20(a). 

Exception: Switch loops shall not require a grounded con- 
ductor. 



(b) Grounded Conductors. Switches or circuit breakers 
shall not disconnect the grounded conductor of a circuit. 

Exception: A switch or circuit breaker shall be permitted 
to disconnect a grounded circuit conductor where all circuit 
conductors are disconnected simultaneously, or where the 
device is arranged so that the grounded conductor cannot 
be disconnected until all the ungrounded conductors of the 
circuit have been disconnected. 

380-3. Enclosure. 

(a) General. Switches and circuit breakers shall be of the 
externally operable type mounted in an enclosure listed for 
the intended use. The minimum wire-bending space at termi- 
nals and minimum gutter space provided in switch enclo- 
sures shall be as required in Section 373-6. 

Exception No. 1: Pendant- and surface-type snap switches 
and knife switches mounted on an open-face switchboard 
or panelboard shall be permitted without enclosures. 

Exception No. 2: Switches and circuit breakers installed in 
accordance with Sections 110-27(a)(l), (2), (3), or (4) shall 
be permitted without enclosures. 

(b) Used as a Raceway. Enclosures shall not be used as 
junction boxes, auxiliary gutters, or raceways for conductors 
feeding through or tapping off to other switches or overcur- 
rent devices, unless the enclosure complies with Section 

373-8. 

380-4. Wet Locations. A switch or circuit breaker in a wet 
location or outside of a building shall be enclosed in a 
weatherproof enclosure or cabinet that shall comply with 
Section 373-2(a). Switches shall not be installed within wet 
locations in tub or shower spaces unless installed as part of 
a listed tub or shower assembly. 

380-5. Time Switches, Flashers, and Similar Devices. 

Time switches, flashers, and similar devices shall be of the 
enclosed type or shall be mounted in cabinets or boxes or 
equipment enclosures. Energized parts shall be barriered to 
prevent operator exposure when making manual adjustments 
or switching. 

Exception: Devices mounted so they are accessible only 
to qualified persons shall be permitted without barriers, 
provided they are located within an enclosure such that 
any energized parts within 6 in. (152 mm) of the manual 
adjustment or switch are covered by suitable barriers. 

380-6. Position and Connection of Switches. 

(a) Single-Throw Knife Switches. Single-throw knife 
switches shall be placed so that gravity will not tend to close 
them. Single-throw knife switches, approved for use in the 



• 



1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 380 — SWITCHES 



70-205 



inverted position, shall be provided with a locking device 
that will ensure that the blades remain in the open position 
when so set. 

(b) Double-Throw Knife Switches. Double-throw knife 
switches shall be permitted to be mounted so that the throw 
will be either vertical or horizontal. Where the throw is 
vertical, a locking device shall be provided to hold the blades 
in the open position when so set. 

(c) Connection of Switches. Single-throw knife switches 
and switches with butt contacts shall be connected so that 
the blades are de-energized when the switch is in the open 
position. Single-throw knife switches, molded-case 
switches, switches with butt contacts, and circuit breakers 
used as switches shall be connected so that the terminals 
supplying the load are de-energized when the switch is in 
the open position. 

Exception: The blades and terminals supplying the load of 
a switch shall be permitted to be energized when the switch 
is in the open position where the switch is connected to 
circuits or equipment inherently capable of providing a back- 
feed source of power. For such installations, a permanent 
sign shall be installed on the switch enclosure or immediately 
adjacent to open switches that reads: 

WARNING — LOAD SIDE TERMINALS MAY BE 
ENERGIZED BY BACKFEED. 

380-7. Indicating. General-use and motor-circuit switches 
and circuit breakers, where mounted in an enclosure as de- 
scribed in Section 380-3, shall clearly indicate whether they 
are in the open (off) or closed (on) position. 

Where these switch or circuit breaker handles are operated 
vertically rather than rotationally or horizontally, the up 
position of the handle shall be the (on) position. 

Exception: Vertically-operated double-throw switches shall 
be permitted to be in the closed (on) position with the handle 
in either the up or down position. 

380-8. Accessibility and Grouping. 

(a) Location. All switches and circuit breakers used as 
switches shall be located so that they may be operated from 
a readily accessible place. They shall be installed so that 
the center of the grip of the operating handle of the switch 
or circuit breaker, when in its highest position, will not be 
more than 6 ft 7 in. (2.0 m) above the floor or working 
platform. 

Exception No. 1: On busway installations, fused switches 
and circuit breakers shall be permitted to be located at the 
same level as the busway. Suitable means shall be provided 
to operate the handle of the device from the floor. 



Exception No. 2: Switches installed adjacent to motors, ap- 
pliances, or other equipment that they supply shall be per- 
mitted to be located higher than specified in the foregoing 
and to be accessible by portable means. 
Exception No. 3: Hookstick operable isolating switches 
shall be permitted at greater heights. 

(b) Voltage Between Adjacent Switches. Snap switches 
shall not be grouped or ganged in enclosures unless they 
can be arranged so that the voltage between adjacent 
switches does not exceed 300, or unless they are installed 
in enclosures equipped with permanently installed barriers 
between adjacent switches. 

380-9. Provisions for Snap Switch Faceplates. 

(a) Position. Snap switches mounted in boxes shall have 
faceplates installed so as to completely cover the opening 
and seat against the finished surface. 

(b) Grounding. Snap switches, including dimmer switches, 
shall be effectively grounded and shall provide a means to 
ground metal faceplates, whether or not a metal faceplate 
is installed. Snap switches shall be considered effectively 
grounded if either of the following conditions are met. 

(1) The switch is mounted with metal screws to a metal 
box or to a nonmetallic box with integral means for ground- 
ing devices. 

(2) An equipment grounding conductor or equipment 
bonding jumper is connected to an equipment grounding 
termination of the snap switch. 

Exception to (b): Where no grounding means exists within 
the snap-switch enclosure or where the wiring method does 
not include or provide an equipment ground, a snap switch 
without a grounding connection shall be permitted for 
replacement purposes only. A snap switch wired under the 
provisions of this exception and located within reach of 
conducting floors or other conducting surfaces shall be 
provided with a faceplate of nonconducting, noncombustible 
material. 

(c) Construction. Metal faceplates shall be of ferrous 
metal not less than 0.030 in. (0.762 mm) in thickness or of 
nonferrous metal not less than 0.040 in. (1.016 mm) in 
thickness. Faceplates of insulating material shall be non- 
combustible and not less than 0.10 in. (2.54 mm) in thick- 
ness, but they shall be permitted to be less than 0.10 in. 
(2.54 mm) in thickness if formed or reinforced to provide 
adequate mechanical strength. 

380-10. Mounting of Snap Switches. 

(a) Surface-Type. Snap switches used with open wiring 
on insulators shall be mounted on insulating material that 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-206 



ARTICLE 380 — SWITCHES 



will separate the conductors at least Vi in. (12.7 mm) from 
the surface wired over. 

(b) Box Mounted. Flush-type snap switches mounted in 
boxes that are set back of the wall surface as permitted in 
Section 370-20 shall be installed so that the extension plaster 
ears are seated against the surface of the wall. Flush-type 
snap switches mounted in boxes that are flush with the wall 
surface or project therefrom shall be installed so that the 
mounting yoke or strap of the switch is seated against the 
box. 

380-11. Circuit Breakers as Switches. A hand-operable 
circuit breaker equipped with a lever or handle, or a power- 
operated circuit breaker capable of being opened by hand 
in the event of a power failure, shall be permitted to serve 
as a switch if it has the required number of poles. 

FPN: See the provisions contained in Sections 240-81 and 
240-83. 

380-12. Grounding of Enclosures. Metal enclosures for 
switches or circuit breakers shall be grounded as specified 
in Article 250. Where nonmetallic enclosures are used with 
metal raceways or metal-armored cables, provisions shall 
be made for grounding continuity. 

Metal boxes for switches shall be effectively grounded. 
Nonmetallic boxes for switches shall be installed with a 
wiring method that provides or includes an equipment 
ground. 

380-13. Knife Switches. 

(a) Isolating Switches. Knife switches rated at over 1200 
amperes at 250 volts or less, and at over 600 amperes at 
251 to 600 volts, shall be used only as isolating switches 
and shall not be opened under load. 

(b) To Interrupt Currents. To interrupt currents over 1200 
amperes at 250 volts, nominal, or less, or over 600 amperes 
at 25 ] to 600 volts, nominal, a circuit breaker or a switch 
of special design listed for such purpose shall be used. 

(c) General-Use Switches. Knife switches of ratings less 
than specified in (a) and (b) shall be considered general-use 
switches. 

FPN: See definition of general-use switch in Article 100. 

(d) Motor-Circuit Switches. Motor-circuit switches shall 
be permitted to be of the knife-switch type. 

FPN: See definition of a motor-circuit switch in Article 100. 

380-14. Rating and Use of Snap Switches. Snap switches 
shall be used within their ratings and as indicated in (a) 
through (d). 



FPN No. 1 : For switches on signs and outline lighting, see 
Section 600-6. 

FPN No. 2: For switches controlling motors, see Sections 
430-83, 430-109, and 430-110. 

(a) Alternating Current General-Use Snap Switch. A 

form of general-use snap switch suitable only for use on ac 
circuits for controlling the following: 

(1) Resistive and inductive loads, including electric- 
discharge lamps, not exceeding the ampere rating of the 
switch at the voltage involved 

(2) Tungsten-filament lamp loads not exceeding the ampere 
rating of the switch at 120 volts 

(3) Motor loads not exceeding 80 percent of the ampere 
rating of the switch at its rated voltage 

(b) Alternating-Current or Direct-Current General-Use 
Snap Switch. A form of general-use snap switch suitable 
for use on either ac or dc circuits for controlling the 
following. 

(1) Resistive loads not exceeding the ampere rating of the 
switch at the voltage applied. 

(2) Inductive loads not exceeding 50 percent of the ampere 
rating of the switch at the applied voltage. Switches 
rated in horsepower are suitable for controlling motor 
loads within their rating at the voltage applied. 

(3) Tungsten-filament lamp loads not exceeding the ampere 
rating of the switch at the applied voltage if T-rated. 

(c) CO/ALR Snap Switches. Snap switches rated 20 am- 
peres or less directly connected to aluminum conductors 
shall be listed and marked CO/ALR. 

(d) Alternating-Current Specific-Use Snap Switches 
Rated for 347 Volts. Snap switches rated 347 volts ac shall 
be listed and shall be used only for controlling the following. 

(1) Noninductive loads other than tungsten-filament 
lamps not exceeding the ampere and voltage ratings of the 
switch. 

(2) Inductive loads not exceeding the ampere and voltage 
ratings of the switch. Where particular load characteristics 
or limitations are specified as a condition of the listing, those 
restrictions shall be observed regardless of the ampere rating 
of the load. 

The ampere rating of the switch shall not be less than 1 5 
amperes at a voltage rating of 347 volts ac. Flush-type snap 
switches rated 347 volts ac shall not be readily interchange- 
able in box mounting with switches identified in Section 
3 80- 14(a) and (b). 



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1999 Edition 



NATIONAL ELECTRfCAL CODE 



ARTICLE 384 — SWITCHBOARDS AND PANELBOARDS 



70-207 



B. Construction Specifications 

380-15. Marking. Switches shall be marked with the cur- 
rent and voltage and, if horsepower rated, the maximum 
rating for which they are designed. 

380-16. 600- Volt Knife Switches. Auxiliary contacts of a 
renewable or quick-break type or the equivalent shall be 
provided on all knife switches rated 600 volts designed for 
use in breaking current over 200 amperes. 

380-17. Fused Switches. A fused switch shall not have 
fuses in parallel except as permitted in Section 240-8. 

380-18. Wire-Bending Space. The wire-bending space re- 
quired by Section 380-3 shall meet Table 373-6(b) spacings 
to the enclosure wall opposite the line and load terminals. 



Article 384 — Switchboards and Panelboards 

A. General 

384-1. Scope. This article covers the following: 

(1) All switchboards, panelboards, and distribution boards 
installed for the control of light and power circuits 

(2) Battery-charging panels supplied from light or power 
circuits 

384-2. Other Articles. Switches, circuit breakers, and 
overcurrent devices used on switchboards, panelboards, and 
distribution boards, and their enclosures, shall comply with 
this article and also with the requirements of Articles 240, 
250, 370, 373, 380, and other articles that apply. Switch- 
boards and panelboards in hazardous (classified) locations 
shall comply with the requirements of Articles 500 through 
517. 

384-3. Support and Arrangement of Busbars and Con- 
ductors. 

(a) Conductors and Busbars on a Switchboard or Panel- 
board. Conductors and busbars on a switchboard or panel-, 
board shall comply with (1), (2), and (3) as applicable. 

(1) Location. Conductors and busbars shall be located 
so as to be free from physical damage and shall be held 
firmly in place. 

(2) Service Switchboards. Barriers shall be placed in 
all service switchboards such that no uninsulated, un- 
grounded service busbar or service terminal will be exposed 
to inadvertent contact by persons or maintenance equipment 
while servicing load terminations. 



I (3) Same Vertical Section. Other than the required in- 
terconnections and control wiring, only those conductors 
that are intended for termination in a vertical section of a 
switchboard shall be located in that section. 

Exception: Conductors shall be permitted to travel horizon- 
tally through vertical sections of switchboards where such 
conductors are isolated from busbars by a barrier. 

(b) Overheating and Inductive Effects. The arrangement 
of busbars and conductors shall be such as to avoid overheat- 
ing due to inductive effects. 

(c) Used as Service Equipment. Each switchboard or 
panelboard, if used as service equipment, shall be provided 
with a main bonding jumper sized in accordance with Section 
250-28(d) or the equivalent placed within the panelboard or 
one of the sections of the switchboard for connecting the 
grounded service conductor on its supply side to the switch- 
board or panelboard frame. All sections of a switchboard 
shall be bonded together using an equipment grounding 
conductor sized in accordance with Table 250-122. 

Exception: Switchboards and panelboards used as service 
equipment on high-impedance grounded-neutral systems in 
accordance with Section 250-36 shall not be required to be 
provided with a main bonding jumper. 

(d) Terminals. In switchboards and panelboards, load ter- 
minals for field wiring, including grounded circuit conductor 
load terminals and connections to the ground bus for load 
equipment grounding conductors, shall be located so that it 
will not be necessary to reach across or beyond an uninsu- 
lated ungrounded line bus in order to make connections. 

(e) High-Leg Marking. On a switchboard or panelboard 
supplied from a 4-wire, delta-connected system where the 
midpoint of one phase winding is grounded, that phase bus- 
bar or conductor having the higher voltage to ground shall 
be durably and permanently marked by an outer finish that 
is orange in color or by other effective means. 

(f) Phase Arrangement. The phase arrangement on 3- 
phase buses shall be A, B, C from front to back, top to 
bottom, or left to right, as viewed from the front of the 
switchboard or panelboard. The B phase shall be that phase 
having the higher voltage to ground on 3-phase, 4-wire, 
delta-connected systems. Other busbar arrangements shall 
be permitted for additions to existing installations and shall 
be marked. 

Exception No 1: Equipment within the same single section 
or multisection switchboard or panelboard as the meter on 
3-phase, 4-wire, delta-connected systems shall be permitted 
to have the same phase configuration as the metering equip- 
ment. 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-208 



ARTICLE 384 — SWITCHBOARDS AND PANELBOARDS 



(g) Minimum Wire-Bending Space. The minimum wire- 
bending space at terminals and minimum gutter space pro- 
vided in panelboards and switchboards shall be as required 
in Section 373-6. 

384-4. Installation. 

FPN: For the dedicated space requirement, see Section 1 10- 

26(f). 

B. Switchboards 

384-5. Location of Switchboards. Switchboards that have 
any exposed live parts shall be located in permanently dry 
locations and then only where under competent supervision 
and accessible only to qualified persons. Switchboards shall 
be located so that the probability of damage from equipment 
or processes is reduced to a minimum. 

384-6. Switchboards in Damp or Wet Locations. Switch- 
boards in damp or wet locations shall be installed to comply 
with Section 373-2(a). 

384-7. Location Relative to Easily Ignitible Material. 

Switchboards shall be placed so as to reduce to a minimum 
the probability of communicating fire to adjacent com- 
bustible materials. Where installed over a combustible floor, 
suitable protection thereto shall be provided. 

384-8. Clearances. 

(a) From Ceiling. For other than a totally enclosed switch- 
board, a space not less than 3 ft (914 mm) shall be provided 
between the top of the switchboard and any combustible 
ceiling, unless a noncombustible shield is provided between 
the switchboard and the ceiling. 

(b) Around Switchboards. Clearances around switch 
boards shall comply with the provisions of Section 1 10-26. 

384-9. Conductor Insulation. An insulated conductor 
used within a switchboard shall be listed, flame retardant, 
and shall be rated not less than the voltage applied to it and 
not less than the voltage applied to other conductors or 
busbars with which it may come in contact. 

384-10. Clearance for Conductors Entering Bus Enclo- 
sures. Where conduits or other raceways enter a switch- 
board, floor-standing panelboard, or similar enclosure at 
the bottom, sufficient space shall be provided to permit 
installation of conductors in the enclosure. The wiring space 
shall not be less than shown in Table 384-10 where the 
conduit or raceways enter or leave the enclosure below the 
busbars, their supports, or other obstructions. The conduit 
or raceways, including their end fittings, shall not rise more 
than 3 in. (76 mm) above the bottom of the enclosure. 



Table 384-10. Clearance for Conductors Entering Bus 
Enclosures 

Minimum Spacing Between 

Bottom of Enclosure and 

Busbars, Their Supports, or 

Other Obstructions 

Conductor in. mm 



• 



Insulated busbars, their supports, 

or other obstructions 
Noninsulated busbars 



10 



203 

254 



384-12. Grounding of Instruments, Relays, Meters, and 
Instrument Transformers on Switchboards. Instruments, 
relays, meters, and instrument transformers located on 
switchboards shall be grounded as specified in Sections 250- 
170 through 250-178. 



C. Panelboards 

384-13. General. All panelboards shall have a rating not 
less than the minimum feeder capacity required for the load 
computed in accordance with Article 220. Panelboards shall 
be durably marked by the manufacturer with the voltage and 
the current rating and the number of phases for which they 
are designed and with the manufacturer's name or trademark 
in such a manner so as to be visible after installation, without 
disturbing the interior parts or wiring. All panelboard circuits 
and circuit modifications shall be legibly identified as to 
purpose or use on a circuit directory located on the face or 
inside of the panel doors. 

FPN: See Section 110-22 for additional requirements. 

384-14. Classification of Panelboards. Panelboards shall 
be classified for the purposes of this article as either lighting 
and appliance branch-circuit panelboards or power pan- 
elboards. 

(a) Lighting and Appliance Branch-Circuit Panelboard. 

A lighting and appliance branch-circuit panelboard is one 
having more than 10 percent of its overcurrent devices 
protecting lighting and appliance branch circuits. A lighting 
and appliance branch circuit is a branch circuit that has a 
connection to the neutral of the panelboard and that has 
overcurrent protection of 30 amperes or less in one or more 
conductors. 

(b) Power Panelboard. A power panelboard is one having 
10 percent or fewer of its overcurrent devices protecting 
lighting and appliance branch circuits. 

384-15. Number of Overcurrent Devices on One Panel- 
board. Not more than 42 overcurrent devices (other than 



• 



1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 384 — SWITCHBOARDS AND PANELBOARDS 



70-209 



those provided for in the mains) of a lighting and appliance 
branch-circuit panelboard shall be installed in any one cabi- 
net or cutout box. 

A lighting and appliance branch-circuit panelboard shall 
be provided with physical means to prevent the installation 
of more overcurrent devices than that number for which the 
panelboard was designed, rated, and approved. 

For the purposes of this article, a 2-pole circuit breaker 
shall be considered two overcurrent devices; a 3-pole circuit 
breaker shall be considered three overcurrent devices. 

384-16. Overcurrent Protection. 

(a) Lighting and Appliance Branch-Circuit Panelboard 
Individually Protected. Each lighting and appliance 
branch-circuit panelboard shall be individually protected on 
the supply side by not more than two main circuit breakers 
or two sets of fuses having a combined rating not greater 
than that of the panelboard. 

Exception No. 1: Individual protection for a lighting and 
appliance panelboard shall not be required if the panelboard 
feeder has overcurrent protection not greater than the rating 
of the panelboard. 

Exception No. 2: For existing installations, individual pro- 
tection for lighting and appliance branch- circuit panel- 
boards shall not be required where such panelboards are 
used as service equipment in supplying an individual resi- 
dential occupancy. 

(b) Power Panelboard Protection. In addition to the re- 
quirements of Section 384-13, a power panelboard with 
supply conductors that include a neutral and having more 
than 10 percent of its overcurrent devices protecting branch 
circuits rated 30 amperes or less shall be protected on the 
supply side by an overcurrent protective device having a 
rating not greater than that of the panelboard. 

Exception: This individual protection shall not be required 
for a power panelboard used as service equipment with 
multiple disconnecting means in accordance with Section 
230-71. 

(c) Snap Switches Rated at 30 Amperes or Less. Panel- 
boards equipped with snap switches rated at 30 amperes or 
less shall have overcurrent protection not in excess of 200 
amperes. 

(d) Continuous Load. The total load on any overcurrent 
device located in a panelboard shall not exceed 80 percent 
of its rating where, in normal operation, the load will con- 
tinue for three hours or more. 

Exception: An assembly, including the overcurrent device, 
shall be permitted to be used for continuous operation at 
100 percent of its rating where it is listed for this purpose. 



(e) Supplied Through a Transformer. Where a panel- 
board is supplied through a transformer, the overcurrent 
protection in 384- 16(a), (b), and (c) shall be located on the 
secondary side of the transformer. 

Exception: A panelboard supplied by the secondary side 
of a transformer shall be considered as protected by the 
overcurrent protection provided on the primary side of the 
transformer where that protection is in accordance with 
Section 240-2 1(c)(1). 

(f) Delta Breakers. A 3-phase disconnect or overcurrent 
device shall not be connected to the bus of any panelboard 
that has less than 3-phase buses. Delta breakers shall not be 
installed in panelboards. 

(g) Back-Fed Devices. Plug-in-type overcurrent protection 
devices or plug-in type main lug assemblies that are back 
fed and used to terminate field-installed ungrounded supply 
conductors shall be secured in place by an additional fastener 
that requires other than a pull to release the device from the 
mounting means on the panel. 

384-17. Panelboards in Damp or Wet Locations. Pan- 
elboards in damp or wet locations shall be installed to comply 
with Section 373-2(a). 

384-18. Enclosure. Panelboards shall be mounted in cabi- 
nets, cutout boxes, or enclosures designed for the purpose 
and shall be dead front. 

Exception: Panelboards other than of the dead-front exter- 
nally operable type shall be permitted where accessible only 
to qualified persons. 

384-19. Relative Arrangement of Switches and Fuses. In 

panelboards, fuses of any type shall be installed on the load 
side of any switches. 

Exception: Fuses installed as part of service equipment in 
accordance with the provisions of Section 230-94 shall be 
permitted on the line side of the service switch. 

384-20. Grounding of Panelboards. Panelboard cabinets 
and panelboard frames, if of metal, shall be in physical 
contact with each other and shall be grounded. Where the 
panelboard is used with nonmetallic raceway or cable or 
where separate grounding conductors are provided, a termi- 
nal bar for the grounding conductors shall be secured inside 
the cabinet. The terminal bar shall be bonded to the cabinet 
and panelboard frame, if of metal, otherwise it shall be 
connected to the grounding conductor that is run with the 
conductors feeding the panelboard. 

Exception: Where an isolated equipment grounding con- 
ductor is provided as permitted by Section 250-146(d), the 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-210 



ARTICLE 384 — SWITCHBOARDS AND PANELBOARDS 



insulated equipment grounding conductor that is run with 
the circuit conductors shall be permitted to pass through 
the panelboard without being connected to the panelboard's 
equipment grounding terminal bar. 

Grounding conductors shall not be connected to a terminal 
bar provided for grounded conductors (may be a neutral) 
unless the bar is identified for the purpose and is located 
where interconnection between equipment grounding con- 
ductors and grounded circuit conductors is permitted or re- 
quired by Article 250. 



D. Construction Specifications 

384-30. Panels. The panels of switchboards shall be made 
of moisture-resistant, noncombustible material. 

384-31. Busbars. Insulated or bare busbars shall be rigidly 
mounted. 

384-32. Protection of Instrument Circuits. Instruments, 
pilot lights, potential transformers, and other switchboard 
devices with potential coils shall be supplied by a circuit 
that is protected by standard overcurrent devices rated 15 
amperes or less. 

Exception No. 1: Overcurrent devices rated more than 15 
amperes shall be permitted where the interruption of the 
circuit could create a hazard. Short-circuit protection shall 
be provided. 

Exception No. 2: For ratings of 2 amperes or less, special 
types of enclosed fuses shall be permitted. 

384-33. Component Parts. Switches, fuses, and fuse- 
holders used on panelboards shall comply with the applicable 
requirements of Articles 240 and 380. 

384-34. Knife Switches. Exposed blades of knife switches 
shall be de-energized when open. 

FPN: See Section 380-6(c), Exception, for installation. 

384-35. Wire-Bending Space in Panelboards. The enclo- 
sure for a panelboard shall have the top and bottom wire- 
bending space sized in accordance with Table 373-6(b) for 
the largest conductor entering or leaving the enclosure. Side 
wire-bending space shall be in accordance with Table 373- 
6(a) for the largest conductor to be terminated in that space. 

Exception No. 1: Either the top or bottom wire-bending 
space shall be permitted to be sized in accordance with 



Table 373-6(a) for a lighting and appliance branch-cir- 
cuit panelboard rated 225 amperes or less. 

Exception No. 2: Either the top or bottom wire-bending 
space for any panelboard shall be permitted to be sized in 
accordance with Table 373-6(a) where at least one side wire- 
bending space is sized in accordance with Table 37 3 -6(b) 
for the largest conductor to be terminated in any side wire- 
bending space. 

Exception No. 3: The top and bottom wire-bending space 
shall be permitted to be sized in accordance with Table 373- 
6(a) spacings if the panelboard is designed and constructed 
for wiring using only one single 90 degree bend for each 
conductor, including the grounded circuit conductor, and the 
wiring diagram shows and specifies the method of wiring 
that shall be used. 

Exception No. 4: Either the top or the bottom wire-bending 
space, but not both, shall be permitted to be sized in accor- 
dance with Table 37 3 -6(a) where there are no conductors 
terminated in that space. 

384-36. Minimum Spacings. The distance between bare 
metal parts, busbars, etc., shall not be less than specified in 
Table 384-36. 

Where close proximity does not cause excessive heating, 
parts of the same polarity at switches, enclosed fuses, etc., 
shall be permitted to be placed as close together as conve- 
nience in handling will allow. 

Exception: The distance shall be permitted to be less than 
that specified in Table 384-36 at circuit breakers and 
switches and in listed components installed in switchboards 
and panelboards. 



Table 384-36. Minimum Spacings Between Bare Metal Parts 



• 







Opposite 










Polarity 










Where 


Opposite 








Mounted on 


Polarity 








the Same 


Where Held 


Live Parts to 






Surface 


Free in Air 


Ground* 


Voltage 




(in.) 


On.) 


(in.) 


Not over 125 


volts, 


V* 


Vi 


'/> 


nominal 










Not over 250 


volts, 


l'/4 


3 /4 


'/2 


nominal 










Not over 600 volts, 


2 


1 


1 


nominal 











• 



Note: For S\ units, 1 in. = 25.4 mm. 

*For spacing between live parts and doors of cabinets, see Sections 373- 

11(a)(1), (2), and (3). 



• 



• 



1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 400 — FLEXIBLE CORDS AND CABLES 



70-211 



CHAPTER 4 
Equipment for General Use 



cords and flexible cables other than those listed in the table 
shall be the subject of special investigation. 



Article 400 — Flexible Cords and Cables 

A. General 

400-1. Scope. This article covers general requirements, ap- 
plications, and construction specifications for flexible cords 
and flexible cables. 

400-2. Other Articles. Flexible cords and flexible cables 
shall comply with this article and with the applicable provi- 
sions of other articles of this Code. 

400-3. Suitability. Flexible cords and cables and their asso- 
ciated fittings shall be suitable for the conditions of use and 
location. 

400-4. Types. Flexible cords and flexible cables shall con- 
form to the description in Table 400-4. Types of flexible 



400-5. Ampacities for Flexible Cords and Cables. Table 
400-5 (A) provides the allowable ampacities and Table 400- 
5(B) provides the ampacities for flexible cords and cables 
with not more than three current-carrying conductors. These 
tables shall be used in conjunction with applicable end-use 
product standards to ensure selection of the proper size and 
type. If the number of current-carrying conductors exceeds 
three, the allowable ampacity or the ampacity of each con- 
ductor shall be reduced from the 3-conductor rating as shown 
in the following table. 



Number of 


Percent of Value in 


Conductors 


Tables 400-5(A) and 400-5(B) 


4-6 


80 


7-9 


70 


10-20 


50 


21-30 


45 


31-40 


40 


41 and above 


■ 35 



Table 400-4. Flexible Cords and Cables (See Section 400-4) 



Nominal Insulation 
Thickness 1 



Trade 
Name 



Type 
Letter 



Size 
(AWG) 



Number of 
Conductors 



Insulation 



AWG 



Mils 



Braid 

on Each 

Conductor 



Outer 
Covering 



Use 



Lamp Cord 


C 


18-10 


2 or more 


Thermset 
or thermo- 
plastic 


18-16 
14-10 


30 

45 


Cotton 


None 


Pendant 
or 
portable - 


Dry 

locations 


Not hard 
usage 


Elevator 
cable 


E 

See 

Note 5. 
See 

Note 9. 
See 
Note 10. 


20-2 


2 or more 


Thermoset 


20-16 
14-12 
12-10 

8-2 


20 
30 
45 
60 


Cotton 


Three 
cotton, 
Outer one 
flame- 
retardant & 
moisture- 
resistant. 
See Note 3. 


Elevator 
lighting 
and 
control 


Nonhazardous locations 




20-16 

14-12 

12-10 

8-2 


20 
30 
45 
60 


Flexible 

nylon 

jacket 




Elevator 


EO 


20-2 


2 or more 


Thermoset 


20-16 


20 


Cotton 


Three 


Elevator 


Nonhaz- 




cable 


See 

Note 5. 
See 
Note i0. 








14-12 

12-10 

8-2 


30- 
45 
60 




cotton, 
Outer one 
flame- 
retardant & 
moisture- 
resistant. 
See Note 3. 


lighting 

and 

control 


ardous 
locations 






One cotton 
and a neo- 
prene 
jacket. 
See Note 3. 


Hazardous 
(classified) 
locations 





(continues) 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-212 



ARTICLE 400 — FLEXIBLE CORDS AND CABLES 



Table 400-4. (Continued) 



Nominal Insulation 
Thickness 1 



Trade 
Name 



Type 
Letter 



Size Number of 
(AWG) Conductors Insulation 



AWG 



Mils 



Braid 

on Each 

Conductor 



Outer 
Covering 



Use 



Elevator 
cable 


ET 

See 

Note 5. 
See 
Note 10. 


20-2 


2 or more 


Thermo- 
plastic 


20-16 20 

14-12 30 

12-10 45 

8-2 60 


Rayon 


Three 
cotton or 
equivalent, 
Outer one 
flame- 
retardant 
& moisture- 
resistant 
See 
Note 3. 


Nonhazardous locations 






ETLB 

See 

Note 5. 
See 
Note 10. 


None 






ETP 

See 

Note 5. 
See 
Note 10. 


Rayon 


Thermo- 
plastic 


Hazardous (classified) locations 




ETT 

See 

Note 5. 
See 
Note 10. 


None 


One cotton 
or equiva- 
lent and a 
thermo- 
plastic 
jacket 




Portable 
power cable 


G 


8-500 
'kcmil 


2-6 plus 
grounding 
conduc- 
tors) 


Thermoset 


8-2 60 
1-4/0 80 

250 kcmil- 95 

500 kcmil 




Oil- 
resistant 
thermoset 


Portable and extra hard usage 




G-GC 


8-500 
kcmil 


3 plus 2 

grounding 

conductors 

and 1 

ground 

check 

conductor 


Thermoset 


8-2 60 
1-4/0 80 

250 kcmil- 95 

500 kcmil 




Oil- 
resistant 
thermoset 




Heater cord 


HPD 


18-12 


2, 3, or 4 


Thermoset 


18-16 15 
14-12 30 


None 


Cotton or 
rayon 


Portable 
heaters 


Dry 
locations 


Not hard 
usage 


Parallel 
heater cord 


HPN 

See 
Note 6. 


18-12 


2 or 3 


Oil- 
resistant 
thermoset 


18-16 45 
14 60 
12 95 


None 


Oil- 
resistant 
thermoset 


Portable 


Damp 
locations 


Not hard 
usage 


Thermoset 
jacketed 
heater 
cords 


HS 


14-12 


2, 3, or 4 


Thermoset 


18-16 30 


None 


Cotton and 
thermoset 


Portable 
or 

portable 
heater 


Damp 


Extra hard 
usage 


HSJ 


18-12 


Hard 
usage 




HSO 


14-12 


Cotton and 
oil- 
resistant 
thermoset 


Extra hard 
usage 




HSJO 


18-12 


Oil- 
resistant 
thermoset 


14-12 45 


Hard 

usage 




HSOO 


14-12 


Extra hard 
usage 




HSJOO 


18-12 


Hard 

usage 


Twisted 
portable 
cord 


PD 


18-10 


2 or more 


Thermoset 
or thermo- 
plastic 


18-16 30 
14-10 45 


Cotton 


Cotton or 
rayon 


Pendant 

or 

portable 


Dry 

locations 


Not hard 
usage 



• 



1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 400 — FLEXIBLE CORDS AND CABLES 



70-213 



Table 400-4. (Continued) 



Nominal Insulation 
Thickness 1 



Trade 
Name 



Type 
Letter 



Size 
(AWG) 



Number of 
Conductors 



Insulation 



AWG 



Mils 



Braid 
on Each Outer 

Conductor Covering 



Use 



Portable 
power cable 


PPE 


8-500 
kcmil 


1-6 plus 
optional 
grounding 
conduc- 
tors) 


Thermo- 
plastic 
elastomer 


8-2 
1-4/0 
250 kcmil- 
500 kcmil 


60 
80 
95 




Oil- 
resistant 
thermo- 
plastic 
elastomer 


Portable, extra hard usage 


Hard 
service cord 


S 

See 
Note 4. 


18-12 


2 or more 


Thermoset 


18-16 

14-10 

8-2 


30 
45 
60 


None 


Thermoset 


Pendant 

or 

portable 


Damp 
locations 


Extra hard 
usage 


Flexible 
stage and 
lighting 
power cable 


SC 


8-250 
kcmil 


1 or more 


8-2 
1-4/0 
250 kcmil 


60. 
80 
95 


Thermoset 2 


Portable, extra hard usage 


SCE 


Thermo- 
plastic 
elastomer 


Thermo- 
plastic 
elastomer 2 






SCT 


Thermo- 
plastic 


Thermo- 
plastic 2 




Hard 
service cord 


SE 

See 
Note 4. 


18-2 


2 or more 


Thermo- 
plastic 
elastomer 


18-16 

14-10 

8-2 ■ 


30 
45 
60 


None 


Thermo- 
plastic 
elastomer 


Pendant 

or 

portable 


Damp 
locations 


Extra hard 
usage 




SEO 

See 
Note 4. 


Oil- 
resistant 
thermo- 
plastic 
elastomer 






SEOO 
See 

Note 4. 


Oil- 
resistant 
thermo- 
plastic 
elastomer 




Junior hard 


SJ 


18-10 


2, 3, 4, or 5 


Thermoset 


18-12 
10 


30 
45 


None 


Thermoset 


Pendant 

or 

portable 


Damp 
locations 


Hard 


cord 


SJE 


Thermo- 
plastic 
elastomer 


Thermo- 
plastic 
elastomer 


usage 




SJEO 


Oil- 
resistant 
thermo- 
plastic 
elastomer 






SJEOO 


Oil- 
resistant 
thermo- 
plastic 
elastomer 








SJO 


Thermoset 


Oil- 
resistant 
thermoset 






SJOO 


Oil- 
resistant 
thermoset 






SJT 


Thermo- 
plastic 


Thermo- 
plastic 





(continues) 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-214 



ARTICLE 400 — FLEXIBLE CORDS AND CABLES 



Table 400-4. (Continued) 



Nominal Insulation 
Thickness 1 



Trade Type Size Number of 

Name Letter (AWG) Conductors Insulation 



AWG 



Mils 



Braid 
on Each Outer 

Conductor Covering 



Use 



Junior hard 


SJTO 


18-10 


2, 3, 4, or 5 


Thermo- 


18-12 


30 


None 


Oil- 


Pendant 


Damp 


Hard 


service 








plastic 








resistant 


or 


locations 


usage 


cord 










10 


45 




thermo- 
plastic 


portable 








SJTOO 


Oil- 












resistant 
























thermo- 
























plastic 


1 














Hard 


SO 


18-2 


2 or more 


Thermoset 


18-16 


. 30 




Oil- 


Pendant 


Damp 


Extra hard 


service cord 


See 
Note 4. 














resistant 
thermoset 


or 
portable 


locations 


usage 




SOO 


Oil- 


14-10 


45 






See 






resistant 


8-2 


60 














Note 4. 






thermoset 
















All thermo- 


SP-1 


20-18 


2 or 3 


Thermoset 


20-18 


30 


None . 


Thermoset 


Pendant 


Damp 


Not hard 


set parallel 
cord 


See 
Note 6. 
















or 
portable 


locations 


usage 




SP-2 


18-16 


18-16 


45 






See 
























Note 6. 
























SP-3 


18-10 


18-16 


60 


Refrig- 






See 








14 


80 






erators, 








Note 6. 








12 
10 


95 
110 






room air 
condi- 
tioners, 
and as 
permit- 
ted in ' 
Section 
422- 
16(b) 






All elas- 


SPE-1 


20-18 


2 or 3 


Thermo- 


20-18 


30 


None 


Thermo- 


Pendant 


Damp 


Not hard 


tomer 


See 






plastic 








plastic 


or 


locations 


usage 


(thermo- 
plastic) 
parallel 
cord 


Note 6. 






elastomer 








elastomer 


portable 






SPE-2 
See 
Note 6. 


18-16 


< 




18-16 


45 














SPE-3 


18-10 


18-16 


60 


Refrig- 






See 








14 


80 






erators, 








Note 6. 








12 
. 10 


95 
110 






room air 
condi- 
tioners, 
and as 
permit- 
ted in 
Section 
422- 
16(b) 






All plastic 


SPT-1 


20-18 


2 or 3 


Thermo- 


20-18 


30 


None 


Thermo- 


Pendant 


Damp 


Not hard 


parallel 
cord 


See 
Note 6. 






plastic 








plastic 


or 
portable 


locations 


usage 




SPT-2 


18-16 


18-16 


45 






See 
























Note 6. 























• 



• 



• 



• 



1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 400 — FLEXIBLE CORDS AND CABLES 



70-215 



Table 400-4. (Continued) 



Nominal Insulation 
Thickness 1 



Trade 
Name 



Type 
Letter 



Size 
(AWG) 



Number of 
Conductors 



Insulation 



AWG 



Mils 



Braid 
on Each Outer 

Conductor Covering 



Use 



AH plastic . 

parallel 

cord 


SPT-3 
See 
Note 6. 


18-10 


2 or 3 


Thermo- 
plastic 


18-16 
14 
12 
10 


60 

80 

95 

110 


None 


Thermo- 
plastic 


Refrig- 
erators, 
room air 
condi- 
tioners, 
and as 
permit- 
ted in 
Section 
422- 
16(6) 


Damp 
locations 


Not hard 
usage 


Range, 
dryer cable 


SRD 


10-4 


3 or 4 


Thermoset 


10-4 


45 


None 


Thermoset 


Portable 


Damp 
locations 


Ranges, 
dryers 




SRDE 


10-4 


3 or 4 


Thermo- 
plastic 
elastomer 


None 


Thermo- 
plastic 
elastomer 


~ 




SRDT 


10-4 


3 or 4 


Thermo- 
plastic 


None 


Thermo- 
plastic 




Hard 
service cord 


ST 
See 
Note 4. 


18-2 


2 or More 


Thermo- 
plastic 


18-16 

14-10 

8-2 


30 
45 
60 


None 


Thermo- 
plastic 


Pendant 

or 

portable 


Damp 
locations 


Extra hard 
usage 




STO 

See 
Note 4. 


Oil- 
resistant 
thermo- 
plastic 






STOO 

See 
Note 4. 


Oil- 
resistant 
thermo- 
plastic 




Vacuum 
cleaner cord 


SV 
See 
Note 6. 


18-16 


2 or 3 


Thermoset 


18-16 


15 


None 


Thermoset 


Pendant 

or 

portable 


Damp 
locations 


Not hard 
usage 




SVE 

See 
Note 6. 


Thermo- 
plastic 
elastomer 


Thermo- 
plastic 
elastomer 






SVEO 
See 
Note 6. 


Oil- 
resistant 
thermo- 
plastic 
elastomer 






SVEOO 

See 
Note 6. 


Oil- 
resistant 
thermo- 
plastic 
elastomer 






svo 


Thermoset 


Oil- 
resistant 
thermoset 






svoo 


Oil- 
resistant 
thermoset 


Oil- 
resistant 

thermoset 






SVT 

See 
Note 6. 


Thermo- 
plastic 


Thermo- 
plastic 





(continues) 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-216 



ARTICLE 400 — FLEXIBLE CORDS AND CABLES 



Table 400-4. (Continued) 



Nominal Insulation 
Thickness 1 



Trade 
Name 



Type Size Number of 

Letter (AWG) Conductors Insulation 



AWG 



Mils 



Braid 
on Each Outer 

Conductor Covering 



Use 



Vacuum 


SVTO 


18-16 


2 or 3 


Thermo- 


18-16 


15 


None 


Oil- 


Pendant 


Damp 


Not hard 


cleaner cord 


See 
Note 6. 






plastic 








resistant 
thermo- 
plastic 


or 
portable 


locations 


usage 




SVTOO 


Oil- 












resistant 
























thermo- 
























plastic 
















Parallel 


TPT 


27 


2 


Thermo- 


27 


30 


None 


Thermo- 


At- 


Damp 


Not hard 


tinsel cord 


See 
Note 2. 






plastic 








plastic 


tached 
to an 
appli- 
ance 


locations 


usage 


Jacketed 


TS 


27 


2 


Thermoset 


27 


15 


None 


Thermoset 


At- 


Damp 


Not hard 


tinsel cord 


See 
Note 2. 
















tached 
to an 
appli- 
ance 


locations 


usage 




TST 


Thermo- 


Thermo- 






See 






plastic 








plastic 










Note 2. 






















Portable 


W 


8-500 


1-6 


Thermoset 


8-2 


60 




Oil- 


Portable, 


extra hard usa 


ge 


power cable 




kcmil 






1-4/0 
250 kcmil- 
500 kcmil 


80 
95 




resistant 
thermoset 








Electric 


EV 


1 8-500 


2 or more 


Thermoset 


18-16 


30 (20) 


Optional 


Thermoset 


Electric 


Wet 


Extra hard 


vehicle 




kcmil 


plus ground- 


with 


14-10 


45 (30) 






vehicle 


locations 


usage 


cable 




See 


ing conduc- 


optional 


8-2 


60 (45) 






charg- 










Note 


tors), plus 


nylon 


1-470 


80 (60) 






ing 










11. 


optional 
hybrid data, 
signal, com- 
muni- 
cations, and 
optical fiber 
cables 


See Note 
12. 


250 kcmil- 
500 kcmil 


95 (75) 
See 
Note 
12. 














EVJ 


18-12 


18-12 


30 (20) 


Hard 






See 








See 










usage 






Note 








Note 
















11. 








12. 














EVE 


18-500 


Thermo- 


18-16 


30 (20) 


Thermo- 


Extra hard 






kcmil 




plastic 


14-10 


45 (30) 




plastic 






usage 






See 




elastomer 


8-2 


60 (45) 




elastomer 












Note 




with 


1-4/0 


80 (60) 
















11. 




optional 
nylon 
See 
Note 12. 


250 kcmil- 
500 kcmil 


95 (75) 
See 
Note 
12. 














EVJE 


18-12 


18-12 


30 (20) 


Hard 






See 








See 










usage 






Note 








Note 
















11. 








12. 













• 



• 



1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 400 — FLEXIBLE CORDS AND CABLES 



70-217 



Table 400-4. (Continued) 



Nominal Insulation 
Thickness 1 



Trade 
Name 



Type 
Letter 



Size 
(AWG) 



Number of 
Conductors 



Insulation 



AWG 



Mils 



Braid 

on Each 

Conductor 



Outer 
Covering 



Use 



Electric 


EVT 


18-500 


2 or more 


Thermo- 


18-16 


30 (20) 


Optional 


Thermo- 


Electric 


Wet 


Extra hard 


vehicle 




kcmil 


plus ground- 


plastic 


14-10 


45 (30) 




plastic 


vehicle 


locations 


usage 


cable 




See 


ing conduc- 


with 


8-2 


60 (45) 






charg- 










Note 


tors), plus 


optional 


1-4A) 


80 (60) 






ing 










11. 


optional 
hybrid data, 
signal, com- 
muni- 
cations, and 
optical fiber 
cables 


nylon 
See Note 
12. 


250 kcmil- 
500 kcmil 


95 (75) 
See 
Note 
12. 














EVJT 


18-12 


18-12 


30 (20) 


Hard 






See 








See 










usage 






Note 








Note 
















11. 








12. , 

i 













J See Note 8. 

2 The required outer covering on some single conductor cables may be integral with the insulation. 

Notes: 

1. Except for Types HPN, SP-1, SP-2, SP-3, SPE-1, SPE-2, SPE-3, SPT-1, SPT-2, SPT-3, TPT, and three-conductor 
parallel versions of SRD, SRDE, SRDT, individual conductors are twisted together. 

2. Types TPT, TS, and TST shall be permitted in lengths not exceeding 8 ft (2.44 m) where attached directly, 
or by means of a special type of plug, to a portable appliance rated at 50 watts or less and of such nature that 
extreme flexibility of the cord is essential. 

3. Rubber-filled or varnished cambric tapes shall be permitted as a substitute for the inner braids. 

4. Types G, G-GC, S, SC, SCE, SCT, SE, SEO, SEOO, SO, SOO, ST, STO, STOO, PPE, and W shall be permitted 
for use on theater stages, in garages, and elsewhere where flexible cords are permitted by this Code. 

5. Elevator traveling cables for operating control and signal circuits shall contain nonmetallic fillers as necessary 
to maintain concentricity. Cables shall have steel supporting members as required for suspension by Section 
620-41. In locations subject to excessive moisture or corrosive vapors or gases, supporting members of other 
materials shall be permitted. Where steel supporting members are used, they shall run straight through the center 
of the cable assembly and shall not be cabled with the copper strands of any conductor. 

In addition to conductors used for control and signaling circuits, Tyes E, EO, ET, ETLB, ETP, and ETT elevator 
cables shall be permitted to incorporate in the construction, one or more No. 20 telephone conductor pairs, one 
or more coaxial cables, or one or more optical fibers. The No. 20 conductor pairs shall be permitted to be covered 
with suitable shielding for telephone, audio, or higher frequency communications circuits; the coaxial cables 
consist of a center conductor, insulation, and shield for use in video or other radio frequency communications 
circuits. The optical fiber shall be suitably covered with flame-retardant thermoplastic. The insulation of the 
conductors shall be rubber or thermoplastic of thickness not less than specified for the other conductors of the 
particular type of cable. Metallic shields shall have their own protective covering. Where used, these components 
shall be permitted to be incorporated in any layer of the cable assembly but shall not run straight through the 
center. 

6. The third conductor in these cables shall be used for equipment grounding purposes only. The insulation of 
the grounding conductor for Types SPE-1, SPE-2, SPE-3, SPT-1, SPT-2, and SPT-3 shall be permitted to be 
thermoset polymer. 

7. The individual conductors of all cords, except those of heat-resistant cords, shall have a thermoset or thermoplas- 
tic insulation, except that the equipment grounding conductor where used shall be in accordance with Section 
400-23(b). 

8. Where the voltage between any two conductors exceeds 300, but does not exceed 600, flexible cord of Nos. 
10 and smaller shall have thermoset or thermoplastic insulation on the individual conductors at least 45 mils in 
thickness, unless Type S, SE, SEO, SEOO, SO, SOO, ST, STO, or STOO cord is used. 

9. Insulations and outer coverings that meet the requirements as flame retardant, limited smoke, and are so listed, 
shall be permitted to be designated limited smoke with the suffix LS after the code type designation. 

10. Elevator cables in sizes No. 20 through 14 are rated 300 volts, and sizes 10 through 2 are rated 600 volts. 
No. 12 is rated 300 volts with a 30 mil-insulation thickness and 600 volts with a 45-mil insulation thickness. 

.11. Conductor size for Types EV, EVJ, EVE, EVJE, EVT, and EVJT cables apply to nonpower-limited circuits 
only. Conductors of power-limited (data, signal, or communications) circuits may extend beyond the stated AWG 
size range. All conductors shall be insulated for the same cable voltage rating. 

12. Insulation thickness for Types EV, EVJ, EVE, EVJE, EVT, and EVJT cables of nylon construction is indicated 
in parentheses. 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-218 



ARTICLE 400 — FLEXIBLE CORDS AND CABLES 



Table 400-5(A). Allowable Ampacity for Flexible Cords and Cables [Based on Ambient 
Temperature of 30°C (86°F). See Section 400-13 and Table 400-4.] 







Thermoset Types 








C, E, EO, PD, S, SJ, SJO, SJOO, 






Thermoset Type 


SO, SOO, SP-1, SP-2, SP-3, SRD, 






TS 


SV, SVO, SVOO 








Thermoplastic Types 








ET, ETLB, ETP, ETT, SE, SEO, 


Types 






SJE, SJEO, SJT, SJTO, SJTOO, 


HPD, HPN, 






SPE-1, SPE-2, SPE-3, SPT-1, 


HS, HSJ, 






SPT-2, SPT-3, ST, 


HSO, HSJO, 


Size 


Thermoplastic 


SRDE, SRDT, STO, STOO, 


HSOO, 


(AWG) 


Types TPT, TST 


SVE, SVEO, SVT, SVTO, SVTOO 


HSJOO 






At Bt 




27* 


0.5 


— — 


— 


20 


— 


5*# *** 


— 


. 18 


— 


7 10 


10 


17 


— 


— • 12 


— 


16 


— 


10 13 


15 


15 


— 


— — 


h 


14 


— 


15 18 


20 


12 


— 


20 25 


30 


10 


— 


25 30 


35 


8 


■ — 


35 40 


— 


6 


— 


45 55 


— 


4 


— 


60 70 


— 


2- 


— 


80 95 


— 



• 



Tinsel cord 

**Elevator cables only . ... 

***7 amperes for elevator cables only; 2 amperes for other types 

fThe allowable currents under subheading A apply to 3-conducfor cords and other multiconductor cords connected 

to utilization equipment so that only 3 conductors are current-carrying. The allowable currents under subheading 

B apply to 2-conductor cords and other multiconductor cords connected to utilization equipment so that only 

2 conductors are current carrying. 



Ultimate Insulation Temperature. In no case shall con- 
ductors be associated together in such a way with respect 
to the kind of circuit, the wiring method used, or the number 
of conductors such that the limiting temperature of the 
conductors is exceeded. 

A neutral conductor that carries only the unbalanced cur- 
rent from other conductors of the same circuit need not be 
considered as a current-carrying conductor. 

In a 3-wire circuit consisting of two phase wires and 
the neutral of a 4-wire, 3-phase wye-connected system, a 
common conductor carries approximately the same current 
as the line-to-neutral currents of the other conductors and 
shall be considered to be a current-carrying conductor. 

On a 4-wire, 3-phase wye circuit where the major portion 
of the load consists of nonlinear loads, there are harmonic 
currents present in the neutral conductor and the neutral 
shall be considered to be a current-carrying conductor. 

An equipment grounding conductor shall not be consid- 
ered a current-carrying conductor. 

Where a single conductor is used for both equipment 
grounding and to carry unbalanced current from other con- 
ductors, as provided for in Section 250-140 for electric 



ranges and electric clothes dryers, it shall not be considered 
as a current-carrying conductor. 

Exception: For other loading conditions, adjustment factors 
shall be permitted to be calculated under Section 3 10-1 5(c). 

FPN: See Appendix B, Table B-310-11 for adjustment fac- 
tors for more than three current-carrying conductors in a 
raceway or cable with load diversity. 

400-6. Markings. 

(a) Standard Markings. Flexible cords and cables shall 
be marked by means of a printed tag attached to the coil 
reel or carton. The tag shall contain the information required 
in Section 310-1 1(a). Types S, SC, SCE, SCT, SE, SEO, 
SEOO, SJ, SJE, SJEO, SJEOO, SJO, SJT, SJTO, SJTOO, 
SO, SOO, ST, STO, and STOO flexible cords and G, G-GC, 
PPE, and W flexible cables shall be durably marked on the 
surface at intervals not exceeding 24 in. (610 mm) with the 
type designation, size, and number of conductors. 

(b) Optional Markings. Flexible cords and cable types 
listed in Table 400-4 shall be permitted to be surface marked 
to indicate special characteristics of the cable materials. 



1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 400 — FLEXIBLE CORDS AND CABLES 



70-219 



Table 400-5(B). Ampacity of Cable Types SC, SCE, SCT, PPE, G, G-GC, and W. [Based on Ambient Temperature of 30°C (86°F). 
See Table 400-4.] 











Temperature Rating of Cable 








Size 
(AWG or 




60°C (140°F) 






75°C (167°F) 






90°C (194°F) 






















kcmil) 


D 1 


E 2 


F 3 


D 1 


E 2 


F 3 


D 1 


E 2 


F 3 


8 


60 


55 


48 


70 


65 


57 


80 


74 


65 


6 


80 


72 


63 


95 


88 


77 


105 


99 


87 


4 


105 


96 


84 


125 


115 


101 


140 


130 


114 


3 


120 


113 


99 


145 


135 


118 


165 


152 


133 


2 


140 


128 


112 


170 


152 


133 


190 


174 


152 


1 


165 


150 


131 


195 


178 


156 


220 


202 


177 


1/0 


195 


173 


151 


230 


207 


181 


260 


234 


205 


2/0 


225 


199 


174 


265 


238 


208 


300 


271 


237 


3/0 


260 


230 


201 


310 


275 


241 


350 


313 


274 


4/0 


300 


265 


232 


360 


317 


277 


405 


361 


316 


250 


340 


296 


259 


405 


354 


310 


455 


402 


352 


300 


375 


330 


289 


445 


395 


346 


505 


449 


393 


350 


420 


363 


318 


505 


435 


381 


570 


495 


433 


400 


455 


392 


343 


545 


469 


410 


615 


535 


468 


500 


515 


448 


392 


620 


537 


470 


700 


613 


536 



The ampacities under subheading D shall be permitted for single-conductor Types SC, SCE, SCT, PPE, and 
W cable only where the individual conductors are not installed in raceways and are not in physical contact 
with each other except in lengths not to exceed 24 in. (610 mm) where passing through the wall of an enclosure. 
2 The ampacities under subheading E apply to two-conductor cables and other multiconductor cables connected 
to utilization equipment so that only two conductors are current carrying. 

3 The ampacities under subheading F apply to three-conductor cables and other multiconductor cables connected 
to utilization equipment so that only three conductors are current carrying. 



FPN: Examples of these markings include, but are not lim- 
ited to, "LS" for limited smoke and markings such as "sun- 
light resistant." 

400-7. Uses Permitted. 

(a) Uses. Flexible cords and cables shall be used only for 
the following: 

(1) Pendants 

(2) Wiring of fixtures 

(3) Connection of portable lamps, portable and mobile 
signs, or appliances 

(4) Elevator cables 

(5) Wiring of cranes and hoists 

(6) Connection of stationary equipment to facilitate their 
frequent interchange 

(7) Prevention of the transmission of noise or vibration 

(8) Appliances where the fastening means and mechanical 
connections are specifically designed to permit ready 
removal for maintenance and repair, and the appliance 
is intended or identified for flexible cord connection 

(9) Data processing cables as permitted by Section 645-5 

(10) Connection of moving parts 

(11) Temporary wiring as permitted in Sections 305-4(b) 
and 305-4(c) 

(b) Attachment Plugs. Where used as permitted in sub- 
sections (a)(3), (a)(6), and (a)(8), each flexible cord shall 



be equipped with an attachment plug and shall be energized 
from a receptacle outlet. 

Exception: As permitted in Section 364-8. 

400-8. Uses Not Permitted. Unless specifically permitted 
in Section 400-7, flexible cords and cables shall not be used 
for the following: 

(1) As a substitute for the fixed wiring of a structure 

(2) Where run through holes in walls, structural ceilings 
suspended ceilings, dropped ceilings, or floors 

(3) Where run through doorways, windows, or similar open- 
ings 

(4) Where attached to building surfaces 

Exception: Flexible cord and cable shall be permitted to 
be attached to building surfaces in accordance with the 
provisions of Section 364-8. 

(5) Where concealed behind building walls, structural ceil- 
ings, suspended ceilings, dropped ceilings, or floors 

(6) Where installed in raceways, except as otherwise permit- 
ted in this Code 

400-9. Splices. Flexible cord shall be used only in contin- 
uous lengths without splice or tap where initially installed 
in applications permitted by Section 400-7(a). The repair of 
hard-service cord and junior hard-service cord (see Trade 
Name column in Table 400-4) No. 14 and larger shall be 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-220 



ARTICLE 400 — FLEXIBLE CORDS AND CABLES 



permitted if conductors are spliced in accordance with Sec- 
tion 110- 14(b) and the completed splice retains the insula- 
tion, outer sheath properties, and usage characteristics of the 
cord being spliced. 

400-10. Pull at Joints and Terminals. Flexible cords and 
cables shall be connected to devices and to fittings so that 
tension will not be transmitted to joints or terminals. 

Exception: Listed portable single pole devices that are in- 
tended to accommodate such tension at their terminals, shall 
be permitted to be used with single conductor flexible cable. 

FPN: Some methods of preventing pull on a cord from 
being transmitted to joints or terminals are knotting the cord, 
winding with tape, and fittings designed for the purpose. 

400-11. In Show Windows and Show Cases. Flexible 
cords used in show windows and show cases shall be Type 
S, SE, SEO, SEOO, SJ, SJE, SJEO, SJEOO, SJO, SJOO, 
SJT, SJTO, SJTOO, SO, SOO, ST, STO, or STOO. 

Exception No. 1: For the wiring of chain-supported lighting 

fixtures. 

Exception No. 2: As supply Cords for portable lamps and 

other merchandise being displayed or exhibited. 

400-12. Minimum Size. The individual conductors of a 
flexible cord or cable shall not be smaller than the sizes in 
Table 400-4. 

Exception: The size of the insulated ground-check conduc- 
tor of Type G-GC cables shall be not smaller than No. 10. 

400-13. Overcurrent Protection. Flexible cords not 
smaller than No. 18, and tinsel cords or cords having equiv- 
alent characteristics of smaller size approved for use with 
specific appliances, shall be considered as protected against 
overcurrent by the overcurrent devices described in Section 
240-4. 

400-14. Protection from Damage. Flexible cords and ca- 
bles shall be protected by bushings or fittings where passing 
through holes in covers, outlet boxes, or similar enclosures. 

B. Construction Specifications 

400-20. Labels. Flexible cords shall be examined and 
tested at the factory and labeled before shipment. 

400-21. Nominal Insulation Thickness. The nominal 
thickness of insulation for conductors of flexible cords and 
cables shall not be less than specified in Table 400-4. 

Exception: The nominal insulation thickness for the ground- 
check conductors of Type G-GC cables shall not be less 
than 45 mils for No. 8 and not less than 30 mils for No. 10. 

400-22. Grounded-Conductor Identification. One con- 
ductor of flexible cords that is intended to be used as a 



grounded circuit conductor shall have a continuous marker 
that readily distinguishes it from the other conductor or 
conductors. The identification shall consist of one of the 
methods indicated in (a) through (f). 

(a) Colored Braid. A braid finished to show a white or 
natural gray color and the braid on the other conductor or 
conductors finished to show a readily distinguishable solid 
color or colors. 

(b) Tracer in Braid. A tracer in a braid of any color con- 
trasting with that of the braid and no tracer in the braid of 
the other conductor or conductors. No tracer shall be used 
in the braid of any conductor of a flexible cord that contains 
a conductor having a braid finished to show white or natural 
gray. 

Exception: In the case of Types C and PD and cords having 
the braids on the individual conductors finished to show 
white or natural gray. In such cords, the identifying marker 
shall be permitted to consist of the solid white or natural 
gray finish on one conductor provided there is a colored 
tracer in the braid of each other conductor. 

(c) Colored Insulation. A white or natural gray insulation 
on one conductor and insulation of a readily distinguishable 
color or colors on the other conductor or conductors for 
cords having no braids on the individual conductors. 

For jacketed cords furnished with appliances, one con- 
ductor having its insulation colored light blue, with the other 
conductors having their insulation of a readily distinguish- 
able color other than white or natural gray. 

Exception: Cords that have insulation on the individual con- 
ductors integral with the jacket. 

The insulation shall be permitted to be covered with an outer 
finish to provide the desired color. 

(d) Colored Separator. A white or natural gray separator 
on one conductor and a separator of a readily distinguishable 
solid color on the other conductor or conductors of cords 
having insulation on the individual conductors integral with 
the jacket. 

(e) Tinned Conductors. One conductor having the indi- 
vidual strands tinned and the other conductor or conductors 
having the individual strands untinned for cords having insu- 
lation on the individual conductors integral with the jacket. 

(f) Surface Marking. One or more stripes, ridges, or 
grooves located on the exterior of the cord so as to identify 
one conductor for cords having insulation on the individual 
conductors integral with the jacket. 

400-23. Equipment Grounding Conductor Identifica- 
tion. A conductor intended to be used as an equipment 
grounding conductor shall have a continuous identifying 



• 



1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 402 — FIXTURE WIRES 



70-221 



• 



marker readily distinguishing it from the other conductor or 
conductors. Conductors having a continuous green color or 
a continuous green color with one or more yellow stripes 
shall not be used for other than equipment grounding pur- 
poses. The identifying marker shall consist of one of the 
methods in (a) or (b). 

(a) Colored Braid. A braid finished to show a continuous 
green color or a continuous green color with one or more 
yellow stripes. 

(b) Colored Insulation or Covering. For cords having no 
braids on the individual conductors, an insulation of a con- 
tinuous green color or a continuous green color with one or 
more yellow stripes. 

400-24. Attachment Plugs. Where a flexible cord is pro- 
vided with an equipment grounding conductor and equipped 
with an attachment plug, the attachment plug shall comply 
with Sections 250-138(a) and (b). 



C. Portable Cables Over 600 Volts, Nominal 

400-30. Scope. This part applies to multiconductor porta- 
ble cables used to connect mobile equipment and machinery. 

400-31. Construction. 

(a) Conductors. The conductors shall be No. 8 copper or 
larger and shall employ flexible stranding. 

Exception: The size of the insulated ground-check conduc- 
tor of Type G-GC cables shall be not smaller than No. 10. 

(b) Shields. Cables operated at over 2000 volts shall be 
shielded. Shielding shall be for the purpose of confining the 
voltage stresses to the insulation. 



(c) Equipment Grounding Conductor(s). An equipment 
grounding cohductor(s) shall be provided. The total area 
shall not be less than that of the size of the equipment 
grounding conductor required in Section 250-122. 

400-32. Shielding. All shields shall be grounded. 

400-33. Grounding. Grounding conductors shall be con- 
nected in accordance with Part E of Article 250. 

400-34. Minimum Bending Radii. The minimum bending 
radii for portable cables during installation and handling in 
service shall be adequate to prevent damage to the cable. 

400-35. Fittings. Connectors used to connect lengths of 
cable in a run shall be of a type that lock firmly together. 
Provisions shall be made to prevent opening or closing these 
connectors while energized. Suitable means shall be used 
to eliminate tension at connectors and terminations. 

400-36. Splices and Terminations. Portable cables shall 
not contain splices unless the splices are of the permanent 
molded, vulcanized types in accordance with Section 
110-14(b). Terminations on portable cables rated over 600 
volts, nominal, shall be accessible only to authorized and 
qualified personnel. 

Article 402 — Fixture Wires 

402-1. Scope. This article covers general requirements and 
construction specifications for fixture wires. 

402-2. Other Articles. Fixture wires shall comply with this 
article and also with the applicable provisions of other arti- 
cles of this Code. 

FPN: For application in lighting fixtures, see Article 410. 

402-3. Types. Fixture wires shall be of a type listed in 
Table 402-3, and they shall comply with all requirements 



Table 402-3. Fixture Wires 



Trade Name 



Thickness of Insulation 



Type 
Letter 



Insulation 



AWG 



Mils 



Outer 
Covering 



Maximum 

Operating 

Temperature 



Application 
Provisions 



Asbestos Covered 


AF 


Impregnated 




Thickness of 


Thickness of 


None 


150°C 


Fixture wiring — 


Heat-resistant 




asbestos or 




Moisture- 


Asbestos 




302°F 


limited to 300 


Fixture Wire 




moisture- 
resistant 
insulation and 
impregnated 
asbestos 


18-14 
12-10 


resistant 

Insulation 

Mils 

20 

25 


Mils 

30 
10 

45 
20 






volts and indoor 
dry locations 


Heat-resistant 


FFH-2 


Heat-resistant 


18-16 


— 


30 


Nonmetallic 


75°C 


Fixture wiring 


Rubber-Covered 




rubber 


18-16 


— ■ 


30 


covering 


167°F 




Fixture Wire — 




Cross-linked 














Flexible Stranding 




synthetic polymer 















NATIONAL ELECTRICAL CODE 



(continues) 
1999 Edition 



70-222 



ARTICLE 402 — FIXTURE WIRES 



Table 402-3. (Continued) 



• 



Trade Name 



Thickness of Insulation 



Type 
Letter 



Insulation AWG 



Mils 



Outer , 
Covering 



Maximum 

Operating 

Temperature 



Application 
Provisions 



ECTFE 

— Solid or 7- 

Strand 


HF 


Ethylene chloro- 
trifluoro-ethylene 


18-14 — 


15- 


None 


150°C 
302°F 


Fixture wiring 


ECTFE 

— Flexible 
Stranding 


HFF 


Ethylene 

ehlorotrifluoro- 

ethylene 


18-14 — 


15 


None 


150°C 
302°F 


Fixture wiring 


Tape Insulated 
Fixture Wire — 
Solid or 7-Strand 


KF-1 
KF-2 


Aromatic 
polyimide tape 

Aromatic 
polyimide tape 


18-10 — 
18-10 — 


5.5 
8.4 


None 
None 


200°C 
392°F 


Fixture wiring — 
limited to 300 
volts 




200°C 
392°F 


Fixture wiring 


Tape Insulated 
Fixture Wire — 
Flexible Stranding 


KFF-1 
KFF-2 


Aromatic 
polyimide tape 

Aromatic 
polyimide tape 


18-10 — 
18-10 — 


5.5 
8.4 


None 
None 


200°C 
392°F 


Fixture wiring — 
limited to 300 
volts 




200°C 
392°F 


Fixture wiring 


Perfluoroalkoxy 
— Solid or 7- 
Strand (Nickel or 
Nickel-Coated 
Copper) 


PAF 


Perfluoroalkoxy 


18-14 — 


20 


None 


250°C 

482°F- 


Fixture wiring 
(nickel or nickel- 
coated copper) 


Perfluoroalkoxy 
— Flexible 
Stranding 


PAFF 


Perfluoroalkoxy 


18-14 — 


20 


None 


150°C 

302°F 


Fixture wiring 


Fluorinated ' 
Ethylene 

Propylene Fixture 
Wire : — Solid or 
7-Strand 


PF 


Fluorinated 

ethylene 

propylene 


18-14 — 


20 


None 


200°C 
392°F 


Fixture wiring 


Fluorinated 
Ethylene 

Propylene Fixture 
Wire — Flexible 
Stranding 


PFF 


Fluorinated 

ethylene 

propylene 


18-14 — 


20 


None 


150°C 
302°F 


Fixture wiring 


Fluorinated 
Ethylene 

Propylene Fixture 
Wire — Solid or 
7-Strand 


PGF 


Fluorinated 

ethylene 

propylene 


18-14 — 


14 


Glass braid 


200°C 
392°F 


Fixture wiring 


Fluorinated 
Ethylene 

Propylene Fixture 
Wire — Flexible 
Stranding 


PGFF 


Fluorinated 

ethylene 

propylene 


18-14 — 


14 


Glass braid 


150°C 
302°F 


Fixture wiring 


Extruded 
Polytetra- 
Fluoroethylene — 
Solid or 7-Strand 
(Nickel or Nickel- 
Coated Copper) 


PTF 


Extruded 
polytetra- 
fluoroethylene 


18-14 — 


20 


None 


250°C 
482°F 


Fixture wiring 
(nickel or nickel- 
coated copper) 


Extruded 
Polytetra- 
Fluoroethylene — 
Flexible Stranding 
26-36 AWG 
(Silver, or Nickel- 
Coated Copper) 


PTFF 


Extruded 

polytetra-. 

fluoroethylene 


18-14 — 


20 


None 


150°C 
302°F 


Fixture wiring 
(silver or nickel- 
coated copper) 



• 



• 



1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 402 — FIXTURE WIRES 



70-223 



Table 402-3. (Continued) 



Thickness of Insulation 



Trade Name 



Type 
Letter 



Insulation 



AWG 



Mils 



Maximum 
Outer Operating Application 

Covering Temperature Provisions 



Heat-resistant 
Rubber-Covered 
Fixture Wire — 
Solid or 7-Strand 


RFH-1 


Heat-resistant 
rubber 


18 — 


15 


Nonmetallic 
covering 


75°C 
167°F 


t 
Fixture wiring — 
limited to 300 
volts 




RFH-2 


Heat-resistant . 
rubber 
Cross-linked 
synthetic polymer 


18-16 — 


30 


None or 

nonmetallic 

covering 


75°C 
167°F 


Fixture wiring 


Heat-resistant 
Cross-Linked 
Synthetic 
Polymer- 
Insulated Fixture 
Wire — Solid or 
Stranded 


RFHH-2* 
RFHH-3* 


Cross- linked 
synthetic polymer 


18-16 — 
18-16 — 


30 
45 


None or 

nonmetallic 

covering 


90°C 
I94°F 


Fixture wiring — 

multiconductor 

cable 


Silicone Insulated 
Fixture Wire — 
Solid or 7-Strand 


SF-1 


Silicone rubber 


18 — 


15 


Nonmetallic 
covering 


200°C 
392°F 


Fixture wiring — 
limited to 300 
volts 




SF-2 


Silicone rubber 


18-14 — 


30 


Nonmetallic 
covering 


200°C 

392°F 


Fixture wiring 


Silicone Insulated 
Fixture Wire — 
Flexible Stranding 


SFF-I 


Silicone rubber 


18 — 


15 


Nonmetallic 
covering 


150°C 
302°F 


Fixture wiring — 
limited to 300 
volts 




SFF-2 


Silicone rubber 


18-14 — 


30 


Nonmetallic 
covering 


I50°C 
302°F 


Fixture wiring 


Thermoplastic 
Covered Fixture 
Wire — Solid or 
7-Strand 


Tp* 


Thermoplastic 


18-16 — 


30 


None 


60°C 
140°F 


Fixture wiring 


Thermoplastic 
Covered Fixture 
Wire — Flexible 
Stranding 


ypp* 


Thermoplastic 


18-16 — 


30 


None 


60°C 
140°F 


Fixture wiring 


Heat-resistant 
Thermoplastic- 
Covered Fixture 
Wire — Solid or 
7-Strand 


TFN* 


Thermoplastic 


18-16 — 


15 


Nylon- 
jacketed or 
equivalent 


90°C 
194°F 


Fixture wiring 


Heat-resistant 
Thermoplastic 
Covered Fixture 
Wire — Flexible 
Stranded 


TFFN* 


Thermoplastic 


18-16 — 


15 


Nylon- 
jacketed or 
equivalent 


90°C 
194°F 


Fixture wiring 


Cross-Linked 
Polyolefin 
Insulated Fixture 
Wire. — Solid or 
7-Strand 


XF* 


Cross-linked 
polyolefin 


18-14 — 
12-10 — 


30 
45 


None 


150°C 
302°F 


Fixture wiring — 
limited to 300 
volts 


Cross-Linked 
Polyolefin 
Insulated Fixture 
Wire — Flexible 
Stranded 


XFF* 


Cross-linked 
polyolefin 


18-14 — 
12-10 — 


. 30 

45 


None 


150°C 
302°F 


Fixture wiring — 
limited to 300 
volts 


Modified ETFE 
— Solid or 7- 
Strand 


ZF 


Modified ethylene 

tetrafluoro- 

ethylene 


18-14 — 


15 


None 


150°C 
302°F 


Fixture wiring 



(continues) 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-224 






ARTICLE 402 — FIXTURE WIRES 








Table 402-3. (Continued) 




Type 
Letter 


Insulation 


Thickness of Insulation 


Outer 
Covering 


Maximum 

Operating 

Temperature 


Application 
Provisions 


Trade Name 


AWG Mils 


Flexible Stranding 


ZFF 


Modified ethylene 

tetrafluoro- 

ethylene 


18-14 — 15 


None 


150°C 
302°F 


Fixture wiring 


High Temp. 
Modified ETFE 
— Solid or 7- 
Strand 


ZHF 


Modified ethylene 

tetrafluoro- 

ethylene 


18-14 — 15 


None 


200°C 
392°F 


Fixture wiring 



*Insulations and outer coverings that meet the requirements of flame retardant, limited smoke and are so listed 
shall be permitted to be designated limited smoke with the suffix ILS after the code type designation. 



• 



of that table. The fixture wires listed in Table 402-3 are all 
suitable for service at 600 volts, nominal, unless otherwise 
specified. 

FPN: Thermoplastic insulation may stiffen at temperatures 
colder than -10°C ( + 14°F), requiring that care be exercised 
during installation at such temperatures. Thermoplastic insu- 
lation may also be deformed at normal temperatures where 
subjected to pressure, requiring care be exercised during 
installation and at points of support. 

402-5. Allowable Ampacities for Fixture Wires. The al- 
lowable ampacity of fixture wire shall be as specified in 
Table 402-5. 

No conductor shall be used under such conditions that 
its operating temperature will exceed the temperature speci- 
fied in Table 402-3 for the type of insulation involved. 

FPN: See Section 3 10-10 for temperature limitation of con- 
ductors. 

Table 402-5. Allowable Ampacity for Fixture Wires 



Size 




(AWG) 


Allowable Ampacity 


18 


6 


16 


8 


14 


17 


12 


23 


10 


28 



402-6. Minimum Size. Fixture wires shall not be smaller 
than No. 18. 

402-7. Number of Conductors in Conduit or Tubing. 

The number of fixture wires permitted in a single conduit 
or tubing shall not exceed the percentage fill specified in 
Table 1, Chapter 9. 

402-8. Grounded Conductor Identification. One con- 
ductor of fixture wires that is intended to be used as a 



grounded conductor shall be identified by means of stripes 
or by the means described in Sections 400-22(a) through (e). 

402-9. Marking. 

(a) Required Information. All fixture wires shall be 
marked to indicate the information required in Section 
310-1 1(a). 

(b) Method of Marking. Thermoplastic insulated fixture 
wire shall be durably marked on the surface at intervals not 
exceeding 24 in. (610 mm). All other fixture wire shall be 
marked by means of a printed tag attached to the coil, reel, 
or carton. 

(c) Optional Marking. Fixture wire types listed in Table 
402-3 shall be permitted to be surface marked to indicate 
special characteristics of the cable materials. 

FPN: Examples of these markings include, but are not lim- 
ited to, "LS" for limited smoke or markings such as "sunlight 
resistant." 



402-10. Uses Permitted. Fixture wires shall be permitted 
(1) for installation in lighting fixtures and in similar equip- 
ment where enclosed or protected and not subject to bending 
or twisting in use, or (2) for connecting lighting fixtures to 
the branch-circuit conductors supplying the fixtures. 

402-11. Uses Not Permitted. Fixture wires shall not be 
used as branch-circuit conductors. 

Exception: As permitted by Section 725-27 for Class 1 cir- 
cuits and Section 760-27 for fire alarm circuits. 

402-12. Overcurrent Protection. Overcurrent protection 
for fixture wires shall be as specified in Section 240-4. 



• 



• 



1999 Edition 



NATIONAL ELECTRICAL CODE 



ARTICLE 410 — LIGHTING FIXTURES, LAMPHOLDERS, LAMPS, AND RECEPTACLES 



70-225 



Article 410 — Lighting Fixtures, Lampholders, 
Lamps, and Receptacles 

A. General 

410-1. Scope. This article covers lighting fixtures, lamp- 
holders, pendants, receptacles, incandescent filament lamps, 
arc lamps, electric-discharge lamps, the wiring and equip- 
ment forming part of such lamps, fixtures, and lighting instal- 
lations. 

FPN: The international term for a lighting fixture is lumi- 
naire and is defined as a complete lighting unit consisting 
of a lamp or lamps together with the parts designed to 
distribute the light, to position and protect the lamps, and 
to connect the lamps to the power supply. 

410-2. Application of Other Articles. Equipment for use 
in hazardous (classified) locations shall conform to Articles 
500 through 517. Lighting systems operating at 30 volts or 
less shall conform to Article 411. Arc lamps used in theaters 
shall comply with Section 520-61, and arc lamps used in 
projection machines shall comply with Section 540-20. Arc 
lamps used on constant-current systems shall comply with 
the general requirements of Article 490. 

410-3. Live Parts. Fixtures, lampholders, lamps, and re- 
ceptacles shall have no live parts normally exposed to con- 
tact. Exposed accessible terminals in lampholders, 
receptacles, and switches shall not be installed in metal 
fixture canopies or in open bases of portable table or floor 
lamps. 

Exception: Cleat-type lampholders and receptacles located 
at least 8 ft (2.44 m) above the floor shall be permitted to 
have exposed terminals. 



B. Fixture Locations 

410-4. Fixtures in Specific Locations. 

(a) Wet and Damp Locations. Fixtures installed in wet or 
damp locations shall be installed so that water cannot enter 
or accumulate in wiring compartments, lampholders, or other 
electrical parts. All fixtures installed in wet locations shall 
be marked, "Suitable for Wet Locations." All fixtures in- 
stalled in damp locations shall be marked, "Suitable for Wet 
Locations" or "Suitable for Damp Locations." 

(b) Corrosive Locations. Fixtures installed in corrosive 
locations shall be of a type suitable for such locations. 

(c) In Ducts or Hoods. Fixtures shall be permitted to be 
installed in commercial cooking hoods where all of the 
following conditions are met. 



(1) The fixture shall be identified for use within commer- 
cial cooking hoods and installed so that the temperature 
limits of the materials used are not exceeded. 

(2) The fixture shall be constructed so that all exhaust 
vapors, grease, oil, or cooking vapors are excluded from the 
lamp and wiring compartment. Diffusers shall be resistant 
to thermal shock. 

(3) Parts of the fixture exposed within the hood shall be 
corrosion resistant or protected against corrosion, and the 
surface shall be smooth so as not to collect deposits and 
facilitate cleaning. 

(4) Wiring methods and materials supplying the fix- 
ture(s) shall not be exposed within the cooking hood. 

FPN: See Section 110-11 for conductors and equipment 
exposed to deteriorating agents. 

(d) Bathtub and Shower Areas. No parts of cord- 
connected fixtures, hanging fixtures, lighting track, pen- 
dants, or ceiling-suspended (paddle) fans shall be located 
within a zone measured 3 ft (914 mm) horizontally and 8 ft 
(2.44 m) vertically from the top of the bathtub rim or shower 
stall threshold. This zone is all encompassing and includes 
the zone directly over the tub or shower stall. 

410-5. Fixtures Near Combustible Material. Fixtures 
shall be constructed, or installed, or equipped with shades 
or guards so that combustible material will not be subjected 
to temperatures in excess of 90°C (194°F). 

410-6. Fixtures Over Combustible Material. Lamp- 
holders installed over highly combustible material shall be 
of the unswitched type. Unless an individual switch is pro- 
vided for each fixture, lampholders shall be located at least 
8 ft (2.44 m) above the floor, or shall be located or guarded 
so that the lamps cannot be readily removed or damaged. 

410-7. Fixtures in Show Windows. Chain-supported fix- 
tures used in a show window shall be permitted to be exter- 
nally wired. No other externally wired fixtures shall be used. 

410-8. Fixtures in Clothes Closets. 
(a) Definition. 

Storage Space. Storage space shall be defined as a vol- 
ume bounded by the sides and back closet walls and planes 
extending from the closet floor vertically to a height of 6 ft 
(1.83 m) or the highest clothes-hanging rod and parallel to 
the walls at a horizontal distance of 24 in. (610 mm) from 
the sides and back of the closet walls respectively, and 
continuing vertically to the closet ceiling parallel to the walls 
at a horizontal distance of 12 in. (305 mm) or the width of 
the shelf, whichever is greater. 



NATIONAL ELECTRICAL CODE 



1999 Edition 



70-226 



ARTICLE 410 — LIGHTING FIXTURES, LAMPHOLDERS, LAMPS, AND RECEPTACLES 



FPN: See Figure 410-8. 



12 in. or 
shelf width 




6 ft or 
rod height 



For SI units: 1 in. = 25.4 mm; 1 ft = 0.3048 m. 
Figure 410-8 Closet storage space. 



For a closet that permits access to both sides of a hanging 
rod, the storage space shall include the volume below the 
highest rod extending 12 in. (305 mm) on either side of the 
rod on a plane horizontal to the floor extending the entire 
length of the rod. 

(b) Fixture Types Permitted. Listed fixtures of the fol- 
lowing types shall be permitted to be installed in a closet: 

(1) A surface-mounted or recessed incandescent fixture with 
a completely enclosed lamp 

(2) A surface-mounted or recessed fluorescent fixture 

(c) Fixture Types Not Permitted. Incandescent fixtures 
with open or partially enclosed lamps and pendant fixtures 
or lampholders shall not be permitted. 

(d) Location. Fixtures in clothes closets shall be permitted 
to be installed as follows. 



(3) Recessed incandescent fixtures with a completely en- 
closed lamp installed in the wall or the ceiling, provided 
there is a minimum clearance of 6 in. (152 mm) between 
the fixture and the nearest point of a storage space. 

(4) Recessed fluorescent fixtures installed in the wall or 
on the ceiling, provided there is a minimum clearance of 6 in. 
(152 mm) between the fixture and the nearest point of a 
storage space. 

410-9. Space for Cove Lighting. Coves shall have ade- 
quate space and shall be located so that lamps and equipment 
can be properly installed and maintained. 

C. Provisions at Fixture Outlet Boxes, Canopies, and 
Pans 

410-10. Space for Conductors. Canopies and outlet boxes 
taken together shall provide adequate space so that fixture 
conductors and their connecting devices can be properly 
installed. 

410-11. Temperature Limit of Conductors in Outlet Box- 
es. Fixtures shall be of such construction or installed so that 
the conductors in outlet boxes shall not be subjected to 
temperatures greater than that for which the conductors are 
rated. 

Branch-circuit wiring, other than 2-wire or multiwire 
branch-circuits supplying